Picture order count reset for multi-layer codecs

ABSTRACT

An apparatus for coding video information according to certain aspects includes a memory unit configured to store video information associated with a plurality of layers and a processor. The processor is configured to obtain information associated with a current access unit (AU) to be coded, the current AU containing pictures from one or more layers of the plurality of layers. The processor is further configured to determine whether the current AU includes a first layer containing an intra random access point (IRAP) picture. The process is additionally configured to reset a picture order count (POC) of the second layer at the current AU, in response to determining that the current AU includes (1) a first layer that contains an IRAP picture and (2) a second layer containing no picture or containing a discardable picture.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/015,346, filed Jun. 20, 2014, which is incorporated by reference inits entirety. Any and all applications for which a foreign or domesticpriority claim is identified in the Application Data Sheet as filed withthe present application are hereby incorporated by reference under 37CFR 1.57.

TECHNICAL FIELD

This disclosure relates to the field of video coding and compression,including both single-layer video coding and multi-layer video coding.Multi-layer video coding can include scalable video coding, multiviewvideo coding, three-dimensional (3D) video coding, etc.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, digital cameras, digital recording devices,digital media players, video gaming devices, video game consoles,cellular or satellite radio telephones, video teleconferencing devices,and the like. Digital video devices implement video compressiontechniques, such as those described in the standards defined by MPEG-2,MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding(AVC), the High Efficiency Video Coding (HEVC) standard, and extensionsof such standards. The video devices may transmit, receive, encode,decode, and/or store digital video information more efficiently byimplementing such video coding techniques.

Video compression techniques perform spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video frame, a portion of a video frame, etc.) maybe partitioned into video blocks, which may also be referred to astreeblocks, coding units (CUs) and/or coding nodes. Video blocks in anintra-coded (I) slice of a picture are encoded using spatial predictionwith respect to reference samples in neighboring blocks in the samepicture. Video blocks in an inter-coded (P or B) slice of a picture mayuse spatial prediction with respect to reference samples in neighboringblocks in the same picture or temporal prediction with respect toreference samples in other reference pictures. Pictures may be referredto as frames, and reference pictures may be referred to as referenceframes.

Spatial or temporal prediction results in a predictive block for a blockto be coded. Residual data represents pixel differences between theoriginal block to be coded and the predictive block. An inter-codedblock is encoded according to a motion vector that points to a block ofreference samples forming the predictive block, and the residual dataindicating the difference between the coded block and the predictiveblock. An intra-coded block is encoded according to an intra-coding modeand the residual data. For further compression, the residual data may betransformed from the pixel domain to a transform domain, resulting inresidual transform coefficients, which then may be quantized. Thequantized transform coefficients, initially arranged in atwo-dimensional array, may be scanned in order to produce aone-dimensional vector of transform coefficients, and entropy encodingmay be applied to achieve even more compression.

SUMMARY

The systems, methods and devices of this disclosure each have severalinnovative aspects, no single one of which is solely responsible for thedesirable attributes disclosed herein. The details of one or moreexamples are set forth in the accompanying drawings and the descriptionbelow, which are not intended to limit the full scope of the inventiveconcepts described herein. Other features, objects, and advantages willbe apparent from the description and drawings, and from the claims.

Scalable video coding (SVC) refers to video coding in which a base layer(BL), sometimes referred to as a reference layer (RL), and one or morescalable enhancement layers (ELs) are used. In SVC, the base layer cancarry video data with a base level of quality. The one or moreenhancement layers can carry additional video data to support, forexample, higher spatial, temporal, and/or signal-to-noise ratio (SNR)levels. Enhancement layers may be defined relative to a previouslyencoded layer. For example, a bottom layer may serve as a BL, while atop layer may serve as an EL. Middle layers may serve as either ELs orRLs, or both. For example, a middle layer (e.g., a layer that is neitherthe lowest layer nor the highest layer) may be an EL for the layersbelow the middle layer, such as the base layer or any interveningenhancement layers, and at the same time serve as a RL for one or moreenhancement layers above the middle layer. Similarly, in the Multiviewor 3D extension of the HEVC standard, there may be multiple views, andinformation of one view may be utilized to code (e.g., encode or decode)the information of another view (e.g., motion estimation, motion vectorprediction and/or other redundancies).

An apparatus for coding video information according to certain aspectsincludes a memory unit and a processor. The memory unit is configured tostore video information associated with a plurality of layers. Theprocessor is configured to obtain information associated with a currentaccess unit (AU) to be coded, the current AU containing pictures fromone or more layers of the plurality of layers. The processor is furtherconfigured to determine whether the current AU includes a first layercontaining an intra random access point (IRAP) picture. The process isadditionally configured to reset a picture order count (POC) of thesecond layer at the current AU, in response to determining that thecurrent AU includes (1) a first layer that contains an IRAP picture and(2) a second layer containing no picture or containing a discardablepicture.

An apparatus for coding video information according to certain aspectsincludes a memory unit and a processor. The memory unit is configured tostore video information associated with a plurality of layers. Theprocessor is configured to obtain information associated with a currentaccess unit (AU) to be coded, the current AU containing pictures fromone or more layers of the plurality of layers. The processor is alsoconfigured to reset a picture order count (POC) of a layer included inthe current AU via (1) resetting only a most significant bit (MSB) ofthe POC or (2) resetting both the MSB of the POC and a least significant(LSB) of the POC. The processor is further configured to, for picturesin one or more Ails subsequent to the current AU in decoding order: seta value of a first flag indicative whether a reset of the POC is a fullreset.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram illustrating an example video encoding anddecoding system that may utilize techniques in accordance with aspectsdescribed in this disclosure.

FIG. 1B is a block diagram illustrating another example video encodingand decoding system that may perform techniques in accordance withaspects described in this disclosure.

FIG. 2A is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 2B is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 3A is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 3B is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 4 is a block diagram illustrating an example configuration ofpictures in different layers.

FIG. 5 is a block diagram illustrating an example configuration ofpictures in different layers.

FIG. 6 is a block diagram illustrating an example configuration ofpictures in different layers.

FIG. 7 is a block diagram illustrating an example configuration ofpictures in different layers.

FIG. 8 is a flowchart illustrating a method of coding video information,according to one or more aspects of the present disclosure.

FIG. 9 is a flowchart illustrating a method of coding video information,according to one or more aspects of the present disclosure.

DETAILED DESCRIPTION

In general, this disclosure relates to single layer coding as well asinter-layer prediction for scalable video coding in the context ofadvanced video codecs, such as HEVC (High Efficiency Video Coding). Morespecifically, the present disclosure relates to systems and methods forpicture order count (POC) reset for multi-layer codecs.

In the description below, H.264/Advanced Video Coding (AVC) techniquesrelated to certain embodiments are described; the HEVC standard andrelated techniques are also discussed. While certain embodiments aredescribed herein in the context of the HEVC and/or H.264 standards, onehaving ordinary skill in the art may appreciate that systems and methodsdisclosed herein may be applicable to any suitable video codingstandard. For example, embodiments disclosed herein may be applicable toone or more of the following standards: International TelecommunicationUnion (ITU) Telecommunication Standardization Sector (ITU-T) H.261,International Organization for Standardization (ISO) and theInternational Electrotechnical Commission (IEC) (ISO/IEC) Moving PictureExperts Group (MPEG) 1 (MPEG-1) Visual, ITU-T H.262 or ISO/IEC MPEG-2Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual and ITU-T H.264 (also knownas ISO/IEC MPEG-4 AVC), including its Scalable Video Coding (SVC) andMultiview Video Coding (MVC) extensions.

HEVC generally follows the framework of previous video coding standardsin many respects. The unit of prediction in HEVC is different from theunits of prediction (e.g., macroblock) in certain previous video codingstandards. In fact, the concept of a macroblock does not exist in HEVCas understood in certain previous video coding standards. A macroblockis replaced by a hierarchical structure based on a quadtree scheme,which may provide high flexibility, among other possible benefits. Forexample, within the HEVC scheme, three types of blocks, Coding Unit(CU), Prediction Unit (PU), and Transform Unit (TU), are defined. CU mayrefer to the basic unit of region splitting. CU may be consideredanalogous to the concept of macroblock, but HEVC does not restrict themaximum size of CUs and may allow recursive splitting into four equalsize CUs to improve the content adaptivity. PU may be considered thebasic unit of inter/intra prediction, and a single PU may containmultiple arbitrary shape partitions to effectively code irregular imagepatterns. TU may be considered the basic unit of transform. TU can bedefined independently from the PU; however, the size of a TU may belimited to the size of the CU to which the TU belongs. This separationof the block structure into three different concepts may allow each unitto be optimized according to the respective role of the unit, which mayresult in improved coding efficiency.

For purposes of illustration only, certain embodiments disclosed hereinare described with examples including only two layers (e.g., a lowerlayer such as the base layer, and a higher layer such as the enhancementlayer) of video data. A “layer” of video data may generally refer to asequence of pictures having at least one common characteristic, such asa view, a frame rate, a resolution, or the like. For example, a layermay include video data associated with a particular view (e.g.,perspective) of multi-view video data. As another example, a layer mayinclude video data associated with a particular layer of scalable videodata. Thus, this disclosure may interchangeably refer to a layer and aview of video data. That is, a view of video data may be referred to asa layer of video data, and a layer of video data may be referred to as aview of video data. In addition, a multi-layer codec (also referred toas a multi-layer video coder or multi-layer encoder-decoder) may jointlyrefer to a multiview codec or a scalable codec (e.g., a codec configuredto encode and/or decode video data using MV-HEVC, 3D-HEVC, SHVC, oranother multi-layer coding technique). Video encoding and video decodingmay both generally be referred to as video coding. It should beunderstood that such examples may be applicable to configurationsincluding multiple base and/or enhancement layers. In addition, for easeof explanation, the following disclosure includes the terms “frames” or“blocks” with reference to certain embodiments. However, these terms arenot meant to be limiting. For example, the techniques described belowcan be used with any suitable video units, such as blocks (e.g., CU, PU,TU, macroblocks, etc.), slices, frames, etc.

Video Coding Standards

A digital image, such as a video image, a TV image, a still image or animage generated by a video recorder or a computer, may consist of pixelsor samples arranged in horizontal and vertical lines. The number ofpixels in a single image is typically in the tens of thousands. Eachpixel typically contains luminance and chrominance information. Withoutcompression, the sheer quantity of information to be conveyed from animage encoder to an image decoder would render real-time imagetransmission impossible. To reduce the amount of information to betransmitted, a number of different compression methods, such as JPEG,MPEG and H.263 standards, have been developed.

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-TH.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual andITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its SVC andMVC extensions.

In addition, a new video coding standard, namely High Efficiency VideoCoding (HEVC), is being developed by the Joint Collaboration Team onVideo Coding (JCT-VC) of ITU-T Video Coding Experts Group (VCEG) andISO/IEC Moving Picture Experts Group (MPEG). The full citation for theHEVC Draft 10 is document JCTVC-L1003, Bross et al., “High EfficiencyVideo Coding (HEVC) Text Specification Draft 10,” Joint CollaborativeTeam on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IECJTC1/SC29/WG11, 12th Meeting: Geneva, Switzerland, Jan. 14, 2013 to Jan.23, 2013. The multiview extension to HEVC, namely MV-HEVC, and thescalable extension to HEVC, named SHVC, are also being developed by theJCT-3V (ITU-T/ISO/IEC Joint Collaborative Team on 3D Video CodingExtension Development) and JCT-VC, respectively.

Overview

The poc_reset_idc syntax element may indicate whether the POC should bereset for a picture. The poc_reset_idc syntax element can indicatewhether the most significant bit (MSB) of the POC should be reset, orboth the MSB and the least significant bit (LSB) of the POC should bereset, or none should be reset. For example, the value of 0 for thepoc_reset_idc indicates that the POC is not reset. The value of 1 forthe poc_reset_idc indicates that the POC MSB should be reset. The valueof 2 for the poc_reset_idc indicates that both the POC MSB and LSBshould be reset. The value of 3 for the poc_reset_idc indicates thatreset was indicated for a previous picture. For example, the value ofpoc_reset_idc for the previous picture was either 1 or 2. The value of 3for poc_reset_idc may be used such that when the picture at which thePOC should be reset is lost (e.g., during the decoding process), the POCcan be properly reset at subsequent pictures.

The full_poc_reset_flag can indicate whether the reset for the previouspicture was only for the POC MSB, or for both the POC MSB and LSB. Forinstance, the value of 0 for the full_poc_reset_flag indicates that onlythe MSB should be reset. The value of 1 for the full_poc_reset_flagindicates that both the MSB and LSB should be reset. Thefull_poc_reset_flag flag can be used in connection with poc_reset_idc.For example, when the value of poc_reset_idc is 3, thefull_poc_reset_flag can indicate whether the POC reset for the previouspicture was for only the MSB or for both the MSB and LSB.

In early versions of SHVC and MV-HEVC (e.g., SHVC Working Draft 6,MV-HEVC Working Draft 8, etc.), certain constraints or restrictionsapply, e.g., with respect to poc_reset_idc. However, these constraintsdo not properly reset the POC when a picture is not present or when apicture is discardable. In addition, in the early versions of SHVC andMV-HEVC, there are no restrictions on the value of full_poc_reset_flagof a picture based on poc_reset_idc of the POC resetting AU in the samePOC resetting period. An incorrect value of full_poc_reset_flag mayresult in the POC reset mechanism not working properly.

In order to address these and other challenges, the techniques accordingto certain aspects reset the POC when a picture is not present (e.g.,missing or absent) or when a picture is discardable. The techniques alsoimpose a restriction on the value of full_poc_reset_flag of a picturebased on the value of poc_reset_idc. In this way, the techniques canmake sure that the POC is reset correctly.

Video Coding System

Various aspects of the novel systems, apparatuses, and methods aredescribed more fully hereinafter with reference to the accompanyingdrawings. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to any specific structureor function presented throughout this disclosure. Rather, these aspectsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the disclosure to those skilled in theart. Based on the teachings herein one skilled in the art shouldappreciate that the scope of the disclosure is intended to cover anyaspect of the novel systems, apparatuses, and methods disclosed herein,whether implemented independently of, or combined with, any other aspectof the present disclosure. For example, an apparatus may be implementedor a method may be practiced using any number of the aspects set forthherein. In addition, the scope of the present disclosure is intended tocover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition toor other than the various aspects of the present disclosure set forthherein. It should be understood that any aspect disclosed herein may beembodied by one or more elements of a claim.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

The attached drawings illustrate examples. Elements indicated byreference numbers in the attached drawings correspond to elementsindicated by like reference numbers in the following description. Inthis disclosure, elements having names that start with ordinal words(e.g., “first,” “second,” “third,” and so on) do not necessarily implythat the elements have a particular order. Rather, such ordinal wordsare merely used to refer to different elements of a same or similartype.

FIG. 1A is a block diagram that illustrates an example video codingsystem 10 that may utilize techniques in accordance with aspectsdescribed in this disclosure. As used described herein, the term “videocoder” refers generically to both video encoders and video decoders. Inthis disclosure, the terms “video coding” or “coding” may refergenerically to video encoding and video decoding. In addition to videoencoders and video decoders, the aspects described in the presentapplication may be extended to other related devices such as transcoders(e.g., devices that can decode a bitstream and re-encode anotherbitstream) and middleboxes (e.g., devices that can modify, transform,and/or otherwise manipulate a bitstream).

As shown in FIG. 1A, video coding system 10 includes a source device 12that generates encoded video data to be decoded at a later time by adestination device 14. In the example of FIG. 1A, the source device 12and destination device 14 constitute separate devices. It is noted,however, that the source and destination devices 12, 14 may be on orpart of the same device, as shown in the example of FIG. 1B.

With reference once again, to FIG. 1A, the source device 12 and thedestination device 14 may respectively comprise any of a wide range ofdevices, including desktop computers, notebook (e.g., laptop) computers,tablet computers, set-top boxes, telephone handsets such as so-called“smart” phones, so-called “smart” pads, televisions, cameras, displaydevices, digital media players, video gaming consoles, video streamingdevice, or the like. In some cases, the source device 12 and thedestination device 14 may be equipped for wireless communication.

The destination device 14 may receive, via link 16, the encoded videodata to be decoded. The link 16 may comprise any type of medium ordevice capable of moving the encoded video data from the source device12 to the destination device 14. In the example of FIG. 1A, the link 16may comprise a communication medium to enable the source device 12 totransmit encoded video data to the destination device 14 in real-time.The encoded video data may be modulated according to a communicationstandard, such as a wireless communication protocol, and transmitted tothe destination device 14. The communication medium may comprise anywireless or wired communication medium, such as a radio frequency (RF)spectrum or one or more physical transmission lines. The communicationmedium may form part of a packet-based network, such as a local areanetwork, a wide-area network, or a global network such as the Internet.The communication medium may include routers, switches, base stations,or any other equipment that may be useful to facilitate communicationfrom the source device 12 to the destination device 14.

Alternatively, encoded data may be output from an output interface 22 toan optional storage device 31. Similarly, encoded data may be accessedfrom the storage device 31 by an input interface 28, for example, of thedestination device 14. The storage device 31 may include any of avariety of distributed or locally accessed data storage media such as ahard drive, flash memory, volatile or non-volatile memory, or any othersuitable digital storage media for storing encoded video data. In afurther example, the storage device 31 may correspond to a file serveror another intermediate storage device that may hold the encoded videogenerated by the source device 12. The destination device 14 may accessstored video data from the storage device 31 via streaming or download.The file server may be any type of server capable of storing encodedvideo data and transmitting that encoded video data to the destinationdevice 14. Example file servers include a web server (e.g., for awebsite), a File Transfer Protocol (FTP) server, network attachedstorage (NAS) devices, or a local disk drive. The destination device 14may access the encoded video data through any standard data connection,including an Internet connection. This may include a wireless channel(e.g., a wireless local area network (WLAN) connection), a wiredconnection (e.g., a digital subscriber line (DSL), a cable modem, etc.),or a combination of both that is suitable for accessing encoded videodata stored on a file server. The transmission of encoded video datafrom the storage device 31 may be a streaming transmission, a downloadtransmission, or a combination of both.

The techniques of this disclosure are not limited to wirelessapplications or settings. The techniques may be applied to video codingin support of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, streaming video transmissions, e.g.,via the Internet (e.g., dynamic adaptive streaming over HypertextTransfer Protocol (HTTP), etc.), encoding of digital video for storageon a data storage medium, decoding of digital video stored on a datastorage medium, or other applications. In some examples, video codingsystem 10 may be configured to support one-way or two-way videotransmission to support applications such as video streaming, videoplayback, video broadcasting, and/or video telephony.

In the example of FIG. 1A, the source device 12 includes a video source18, a video encoder 20 and the output interface 22. In some cases, theoutput interface 22 may include a modulator/demodulator (modem) and/or atransmitter. In the source device 12, the video source 18 may include asource such as a video capture device, e.g., a video camera, a videoarchive containing previously captured video, a video feed interface toreceive video from a video content provider, and/or a computer graphicssystem for generating computer graphics data as the source video, or acombination of such sources. As one example, if the video source 18 is avideo camera, the source device 12 and the destination device 14 mayform so-called “camera phones” or “video phones,” as illustrated in theexample of FIG. 1B. However, the techniques described in this disclosuremay be applicable to video coding in general, and may be applied towireless and/or wired applications.

The captured, pre-captured, or computer-generated video may be encodedby the video encoder 20. The encoded video data may be transmitted tothe destination device 14 via the output interface 22 of the sourcedevice 12. The encoded video data may also (or alternatively) be storedonto the storage device 31 for later access by the destination device 14or other devices, for decoding and/or playback. The video encoder 20illustrated in FIGS. 1A and 1B may comprise the video encoder 20illustrated FIG. 2A, the video encoder 23 illustrated in FIG. 2B, or anyother video encoder described herein.

In the example of FIG. 1A, the destination device 14 includes an inputinterface 28, a video decoder 30, and a display device 32. In somecases, the input interface 28 may include a receiver and/or a modem. Theinput interface 28 of the destination device 14 may receive the encodedvideo data over the link 16 and/or from the storage device 31. Theencoded video data communicated over the link 16, or provided on thestorage device 31, may include a variety of syntax elements generated bythe video encoder 20 for use by a video decoder, such as the videodecoder 30, in decoding the video data. Such syntax elements may beincluded with the encoded video data transmitted on a communicationmedium, stored on a storage medium, or stored a file server. The videodecoder 30 illustrated in FIGS. 1A and 1B may comprise the video decoder30 illustrated FIG. 3A, the video decoder 33 illustrated in FIG. 3B, orany other video decoder described herein.

The display device 32 may be integrated with, or external to, thedestination device 14. In some examples, the destination device 14 mayinclude an integrated display device and also be configured to interfacewith an external display device. In other examples, the destinationdevice 14 may be a display device. In general, the display device 32displays the decoded video data to a user, and may comprise any of avariety of display devices such as a liquid crystal display (LCD), aplasma display, an organic light emitting diode (OLED) display, oranother type of display device.

In related aspects, FIG. 1B shows an example video encoding and decodingsystem 10′ wherein the source and destination devices 12, 14 are on orpart of a device 11. The device 11 may be a telephone handset, such as a“smart” phone or the like. The device 11 may include an optionalcontroller/processor device 13 in operative communication with thesource and destination devices 12, 14. The system 10′ of FIG. 1B, andcomponents thereof, are otherwise similar to the system 10 of FIG. 1A,and components thereof.

The video encoder 20 and the video decoder 30 may operate according to avideo compression standard, such as the HEVC, and may conform to a HEVCTest Model (HM). Alternatively, the video encoder 20 and video decoder30 may operate according to other proprietary or industry standards,such as the ITU-T H.264 standard, alternatively referred to as MPEG-4,Part 10, AVC, or extensions of such standards. The techniques of thisdisclosure, however, are not limited to any particular coding standard.Other examples of video compression standards include MPEG-2 and ITU-TH.263.

Although not shown in the examples of FIGS. 1A and 1B, the video encoder20 and the video decoder 30 may each be integrated with an audio encoderand decoder, and may include appropriate MUX-DEMUX units, or otherhardware and software, to handle encoding of both audio and video in acommon data stream or separate data streams. If applicable, in someexamples, MUX-DEMUX units may conform to the ITU H.223 multiplexerprotocol, or other protocols such as the user datagram protocol (UDP).

The video encoder 20 and the video decoder 30 each may be implemented asany of a variety of suitable encoder circuitry, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),discrete logic, software, hardware, firmware or any combinationsthereof. When the techniques are implemented partially in software, adevice may store instructions for the software in a suitable,non-transitory computer-readable medium and execute the instructions inhardware using one or more processors to perform the techniques of thisdisclosure. Each of the video encoder 20 and the video decoder 30 may beincluded in one or more encoders or decoders, either of which may beintegrated as part of a combined encoder/decoder (CODEC) in a respectivedevice.

Video Coding Process

As mentioned briefly above, the video encoder 20 encodes video data. Thevideo data may comprise one or more pictures. Each of the pictures is astill image forming part of a video. In some instances, a picture may bereferred to as a video “frame.” When the video encoder 20 encodes thevideo data, the video encoder 20 may generate a bitstream. The bitstreammay include a sequence of bits that form a coded representation of thevideo data. The bitstream may include coded pictures and associateddata. A coded picture is a coded representation of a picture.

To generate the bitstream, the video encoder 20 may perform encodingoperations on each picture in the video data. When the video encoder 20performs encoding operations on the pictures, the video encoder 20 maygenerate a series of coded pictures and associated data. The associateddata may include video parameter sets (VPS), sequence parameter sets(SPSs), picture parameter sets (PPSs), adaptation parameter sets (APSs),and other syntax structures. A SPS may contain parameters applicable tozero or more sequences of pictures. A PPS may contain parametersapplicable to zero or more pictures. An APS may contain parametersapplicable to zero or more pictures. Parameters in an APS may beparameters that are more likely to change than parameters in a PPS.

To generate a coded picture, the video encoder 20 may partition apicture into equally-sized video blocks. A video block may be atwo-dimensional array of samples. Each of the video blocks is associatedwith a treeblock. In some instances, a treeblock may be referred to as alargest coding unit (LCU). The treeblocks of HEVC may be broadlyanalogous to the macroblocks of previous standards, such as H.264/AVC.However, a treeblock is not necessarily limited to a particular size andmay include one or more coding units (CUs). The video encoder 20 may usequadtree partitioning to partition the video blocks of treeblocks intovideo blocks associated with CUs, hence the name “treeblocks.”

In some examples, the video encoder 20 may partition a picture into aplurality of slices. Each of the slices may include an integer number ofCUs. In some instances, a slice comprises an integer number oftreeblocks. In other instances, a boundary of a slice may be within atreeblock.

As part of performing an encoding operation on a picture, the videoencoder 20 may perform encoding operations on each slice of the picture.When the video encoder 20 performs an encoding operation on a slice, thevideo encoder 20 may generate encoded data associated with the slice.The encoded data associated with the slice may be referred to as a“coded slice.”

To generate a coded slice, the video encoder 20 may perform encodingoperations on each treeblock in a slice. When the video encoder 20performs an encoding operation on a treeblock, the video encoder 20 maygenerate a coded treeblock. The coded treeblock may comprise datarepresenting an encoded version of the treeblock.

When the video encoder 20 generates a coded slice, the video encoder 20may perform encoding operations on (e.g., encode) the treeblocks in theslice according to a raster scan order. For example, the video encoder20 may encode the treeblocks of the slice in an order that proceeds fromleft to right across a topmost row of treeblocks in the slice, then fromleft to right across a next lower row of treeblocks, and so on until thevideo encoder 20 has encoded each of the treeblocks in the slice.

As a result of encoding the treeblocks according to the raster scanorder, the treeblocks above and to the left of a given treeblock mayhave been encoded, but treeblocks below and to the right of the giventreeblock have not yet been encoded. Consequently, the video encoder 20may be able to access information generated by encoding treeblocks aboveand to the left of the given treeblock when encoding the giventreeblock. However, the video encoder 20 may be unable to accessinformation generated by encoding treeblocks below and to the right ofthe given treeblock when encoding the given treeblock.

To generate a coded treeblock, the video encoder 20 may recursivelyperform quadtree partitioning on the video block of the treeblock todivide the video block into progressively smaller video blocks. Each ofthe smaller video blocks may be associated with a different CU. Forexample, the video encoder 20 may partition the video block of atreeblock into four equally-sized sub-blocks, partition one or more ofthe sub-blocks into four equally-sized sub-sub-blocks, and so on. Apartitioned CU may be a CU whose video block is partitioned into videoblocks associated with other CUs. A non-partitioned CU may be a CU whosevideo block is not partitioned into video blocks associated with otherCUs.

One or more syntax elements in the bitstream may indicate a maximumnumber of times the video encoder 20 may partition the video block of atreeblock. A video block of a CU may be square in shape. The size of thevideo block of a CU (e.g., the size of the CU) may range from 8×8 pixelsup to the size of a video block of a treeblock (e.g., the size of thetreeblock) with a maximum of 64×64 pixels or greater.

The video encoder 20 may perform encoding operations on (e.g., encode)each CU of a treeblock according to a z-scan order. In other words, thevideo encoder 20 may encode a top-left CU, a top-right CU, a bottom-leftCU, and then a bottom-right CU, in that order. When the video encoder 20performs an encoding operation on a partitioned CU, the video encoder 20may encode CUs associated with sub-blocks of the video block of thepartitioned CU according to the z-scan order. In other words, the videoencoder 20 may encode a CU associated with a top-left sub-block, a CUassociated with a top-right sub-block, a CU associated with abottom-left sub-block, and then a CU associated with a bottom-rightsub-block, in that order.

As a result of encoding the CUs of a treeblock according to a z-scanorder, the CUs above, above-and-to-the-left, above-and-to-the-right,left, and below-and-to-the left of a given CU may have been encoded. CUsbelow and to the right of the given CU have not yet been encoded.Consequently, the video encoder 20 may be able to access informationgenerated by encoding some CUs that neighbor the given CU when encodingthe given CU. However, the video encoder 20 may be unable to accessinformation generated by encoding other CUs that neighbor the given CUwhen encoding the given CU.

When the video encoder 20 encodes a non-partitioned CU, the videoencoder 20 may generate one or more prediction units (PUs) for the CU.Each of the PUs of the CU may be associated with a different video blockwithin the video block of the CU. The video encoder 20 may generate apredicted video block for each PU of the CU. The predicted video blockof a PU may be a block of samples. The video encoder 20 may use intraprediction or inter prediction to generate the predicted video block fora PU.

When the video encoder 20 uses intra prediction to generate thepredicted video block of a PU, the video encoder 20 may generate thepredicted video block of the PU based on decoded samples of the pictureassociated with the PU. If the video encoder 20 uses intra prediction togenerate predicted video blocks of the PUs of a CU, the CU is anintra-predicted CU. When the video encoder 20 uses inter prediction togenerate the predicted video block of the PU, the video encoder 20 maygenerate the predicted video block of the PU based on decoded samples ofone or more pictures other than the picture associated with the PU. Ifthe video encoder 20 uses inter prediction to generate predicted videoblocks of the PUs of a CU, the CU is an inter-predicted CU.

Furthermore, when the video encoder 20 uses inter prediction to generatea predicted video block for a PU, the video encoder 20 may generatemotion information for the PU. The motion information for a PU mayindicate one or more reference blocks of the PU. Each reference block ofthe PU may be a video block within a reference picture. The referencepicture may be a picture other than the picture associated with the PU.In some instances, a reference block of a PU may also be referred to asthe “reference sample” of the PU. The video encoder 20 may generate thepredicted video block for the PU based on the reference blocks of thePU.

After the video encoder 20 generates predicted video blocks for one ormore PUs of a CU, the video encoder 20 may generate residual data forthe CU based on the predicted video blocks for the PUs of the CU. Theresidual data for the CU may indicate differences between samples in thepredicted video blocks for the PUs of the CU and the original videoblock of the CU.

Furthermore, as part of performing an encoding operation on anon-partitioned CU, the video encoder 20 may perform recursive quadtreepartitioning on the residual data of the CU to partition the residualdata of the CU into one or more blocks of residual data (e.g., residualvideo blocks) associated with transform units (TUs) of the CU. Each TUof a CU may be associated with a different residual video block.

The video encoder 20 may apply one or more transforms to residual videoblocks associated with the TUs to generate transform coefficient blocks(e.g., blocks of transform coefficients) associated with the TUs.Conceptually, a transform coefficient block may be a two-dimensional(2D) matrix of transform coefficients.

After generating a transform coefficient block, the video encoder 20 mayperform a quantization process on the transform coefficient block.Quantization generally refers to a process in which transformcoefficients are quantized to possibly reduce the amount of data used torepresent the transform coefficients, providing further compression. Thequantization process may reduce the bit depth associated with some orall of the transform coefficients. For example, an n-bit transformcoefficient may be rounded down to an m-bit transform coefficient duringquantization, where n is greater than m.

The video encoder 20 may associate each CU with a quantization parameter(QP) value. The QP value associated with a CU may determine how thevideo encoder 20 quantizes transform coefficient blocks associated withthe CU. The video encoder 20 may adjust the degree of quantizationapplied to the transform coefficient blocks associated with a CU byadjusting the QP value associated with the CU.

After the video encoder 20 quantizes a transform coefficient block, thevideo encoder 20 may generate sets of syntax elements that represent thetransform coefficients in the quantized transform coefficient block. Thevideo encoder 20 may apply entropy encoding operations, such as ContextAdaptive Binary Arithmetic Coding (CABAC) operations, to some of thesesyntax elements. Other entropy coding techniques such as contextadaptive variable length coding (CAVLC), probability intervalpartitioning entropy (PIPE) coding, or other binary arithmetic codingcould also be used.

The bitstream generated by the video encoder 20 may include a series ofNetwork Abstraction Layer (NAL) units. Each of the NAL units may be asyntax structure containing an indication of a type of data in the NALunit and bytes containing the data. For example, a NAL unit may containdata representing a video parameter set, a sequence parameter set, apicture parameter set, a coded slice, supplemental enhancementinformation (SEI), an access unit delimiter, filler data, or anothertype of data. The data in a NAL unit may include various syntaxstructures.

The video decoder 30 may receive the bitstream generated by the videoencoder 20. The bitstream may include a coded representation of thevideo data encoded by the video encoder 20. When the video decoder 30receives the bitstream, the video decoder 30 may perform a parsingoperation on the bitstream. When the video decoder 30 performs theparsing operation, the video decoder 30 may extract syntax elements fromthe bitstream. The video decoder 30 may reconstruct the pictures of thevideo data based on the syntax elements extracted from the bitstream.The process to reconstruct the video data based on the syntax elementsmay be generally reciprocal to the process performed by the videoencoder 20 to generate the syntax elements.

After the video decoder 30 extracts the syntax elements associated witha CU, the video decoder 30 may generate predicted video blocks for thePUs of the CU based on the syntax elements. In addition, the videodecoder 30 may inverse quantize transform coefficient blocks associatedwith TUs of the CU. The video decoder 30 may perform inverse transformson the transform coefficient blocks to reconstruct residual video blocksassociated with the TUs of the CU. After generating the predicted videoblocks and reconstructing the residual video blocks, the video decoder30 may reconstruct the video block of the CU based on the predictedvideo blocks and the residual video blocks. In this way, the videodecoder 30 may reconstruct the video blocks of CUs based on the syntaxelements in the bitstream.

Video Encoder

FIG. 2A is a block diagram illustrating an example of the video encoder20 that may implement techniques in accordance with aspects described inthis disclosure. The video encoder 20 may be configured to process asingle layer of a video frame, such as for HEVC. Further, the videoencoder 20 may be configured to perform any or all of the techniques ofthis disclosure, including but not limited to the methods of inferringNoOutputOfPriorPicsFlag and related processes described in greaterdetail above and below with respect to FIGS. 4 and 5. As one example,prediction processing unit 100 may be configured to perform any or allof the techniques described in this disclosure. In another embodiment,the video encoder 20 includes an optional inter-layer prediction unit128 that is configured to perform any or all of the techniques describedin this disclosure. In other embodiments, inter-layer prediction can beperformed by prediction processing unit 100 (e.g., inter prediction unit121 and/or intra prediction unit 126), in which case the inter-layerprediction unit 128 may be omitted. However, aspects of this disclosureare not so limited. In some examples, the techniques described in thisdisclosure may be shared among the various components of the videoencoder 20. In some examples, additionally or alternatively, a processor(not shown) may be configured to perform any or all of the techniquesdescribed in this disclosure.

For purposes of explanation, this disclosure describes the video encoder20 in the context of HEVC coding. However, the techniques of thisdisclosure may be applicable to other coding standards or methods. Theexample depicted in FIG. 2A is for a single layer codec. However, aswill be described further with respect to FIG. 2B, some or all of thevideo encoder 20 may be duplicated for processing of a multi-layercodec.

The video encoder 20 may perform intra- and inter-coding of video blockswithin video slices. Intra coding relies on spatial prediction to reduceor remove spatial redundancy in video within a given video frame orpicture. Inter-coding relies on temporal prediction to reduce or removetemporal redundancy in video within adjacent frames or pictures of avideo sequence. Intra-mode (I mode) may refer to any of several spatialbased coding modes. Inter-modes, such as uni-directional prediction (Pmode) or bi-directional prediction (B mode), may refer to any of severaltemporal-based coding modes.

In the example of FIG. 2A, the video encoder 20 includes a plurality offunctional components. The functional components of the video encoder 20include a prediction processing unit 100, a residual generation unit102, a transform processing unit 104, a quantization unit 106, aninverse quantization unit 108, an inverse transform unit 110, areconstruction unit 112, a filter unit 113, a decoded picture buffer114, and an entropy encoding unit 116. Prediction processing unit 100includes an inter prediction unit 121, a motion estimation unit 122, amotion compensation unit 124, an intra prediction unit 126, and aninter-layer prediction unit 128. In other examples, the video encoder 20may include more, fewer, or different functional components.Furthermore, motion estimation unit 122 and motion compensation unit 124may be highly integrated, but are represented in the example of FIG. 2Aseparately for purposes of explanation.

The video encoder 20 may receive video data. The video encoder 20 mayreceive the video data from various sources. For example, the videoencoder 20 may receive the video data from video source 18 (e.g., shownin FIG. 1A or 1B) or another source. The video data may represent aseries of pictures. To encode the video data, the video encoder 20 mayperform an encoding operation on each of the pictures. As part ofperforming the encoding operation on a picture, the video encoder 20 mayperform encoding operations on each slice of the picture. As part ofperforming an encoding operation on a slice, the video encoder 20 mayperform encoding operations on treeblocks in the slice.

As part of performing an encoding operation on a treeblock, predictionprocessing unit 100 may perform quadtree partitioning on the video blockof the treeblock to divide the video block into progressively smallervideo blocks. Each of the smaller video blocks may be associated with adifferent CU. For example, prediction processing unit 100 may partitiona video block of a treeblock into four equally-sized sub-blocks,partition one or more of the sub-blocks into four equally-sizedsub-sub-blocks, and so on.

The sizes of the video blocks associated with CUs may range from 8×8samples up to the size of the treeblock with a maximum of 64×64 samplesor greater. In this disclosure, “N×N” and “N by N” may be usedinterchangeably to refer to the sample dimensions of a video block interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 video block has sixteen samples in avertical direction (y=16) and sixteen samples in a horizontal direction(x=16). Likewise, an N×N block generally has N samples in a verticaldirection and N samples in a horizontal direction, where N represents anonnegative integer value.

Furthermore, as part of performing the encoding operation on atreeblock, prediction processing unit 100 may generate a hierarchicalquadtree data structure for the treeblock. For example, a treeblock maycorrespond to a root node of the quadtree data structure. If predictionprocessing unit 100 partitions the video block of the treeblock intofour sub-blocks, the root node has four child nodes in the quadtree datastructure. Each of the child nodes corresponds to a CU associated withone of the sub-blocks. If prediction processing unit 100 partitions oneof the sub-blocks into four sub-sub-blocks, the node corresponding tothe CU associated with the sub-block may have four child nodes, each ofwhich corresponds to a CU associated with one of the sub-sub-blocks.

Each node of the quadtree data structure may contain syntax data (e.g.,syntax elements) for the corresponding treeblock or CU. For example, anode in the quadtree may include a split flag that indicates whether thevideo block of the CU corresponding to the node is partitioned (e.g.,split) into four sub-blocks. Syntax elements for a CU may be definedrecursively, and may depend on whether the video block of the CU issplit into sub-blocks. A CU whose video block is not partitioned maycorrespond to a leaf node in the quadtree data structure. A codedtreeblock may include data based on the quadtree data structure for acorresponding treeblock.

The video encoder 20 may perform encoding operations on eachnon-partitioned CU of a treeblock. When the video encoder 20 performs anencoding operation on a non-partitioned CU, the video encoder 20generates data representing an encoded representation of thenon-partitioned CU.

As part of performing an encoding operation on a CU, predictionprocessing unit 100 may partition the video block of the CU among one ormore PUs of the CU. The video encoder 20 and the video decoder 30 maysupport various PU sizes. Assuming that the size of a particular CU is2N×2N, the video encoder 20 and the video decoder 30 may support PUsizes of 2N×2N or N×N, and inter-prediction in symmetric PU sizes of2N×2N, 2N×N, N×2N, N×N, 2N×nU, nL×2N, nR×2N, or similar. The videoencoder 20 and the video decoder 30 may also support asymmetricpartitioning for PU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N. In someexamples, prediction processing unit 100 may perform geometricpartitioning to partition the video block of a CU among PUs of the CUalong a boundary that does not meet the sides of the video block of theCU at right angles.

Inter prediction unit 121 may perform inter prediction on each PU of theCU. Inter prediction may provide temporal compression. To perform interprediction on a PU, motion estimation unit 122 may generate motioninformation for the PU. Motion compensation unit 124 may generate apredicted video block for the PU based the motion information anddecoded samples of pictures other than the picture associated with theCU (e.g., reference pictures). In this disclosure, a predicted videoblock generated by motion compensation unit 124 may be referred to as aninter-predicted video block.

Slices may be I slices, P slices, or B slices. Motion estimation unit122 and motion compensation unit 124 may perform different operationsfor a PU of a CU depending on whether the PU is in an I slice, a Pslice, or a B slice. In an I slice, all PUs are intra predicted. Hence,if the PU is in an I slice, motion estimation unit 122 and motioncompensation unit 124 do not perform inter prediction on the PU.

If the PU is in a P slice, the picture containing the PU is associatedwith a list of reference pictures referred to as “list 0.” Each of thereference pictures in list 0 contains samples that may be used for interprediction of other pictures. When motion estimation unit 122 performsthe motion estimation operation with regard to a PU in a P slice, motionestimation unit 122 may search the reference pictures in list 0 for areference block for the PU. The reference block of the PU may be a setof samples, e.g., a block of samples, that most closely corresponds tothe samples in the video block of the PU. Motion estimation unit 122 mayuse a variety of metrics to determine how closely a set of samples in areference picture corresponds to the samples in the video block of a PU.For example, motion estimation unit 122 may determine how closely a setof samples in a reference picture corresponds to the samples in thevideo block of a PU by sum of absolute difference (SAD), sum of squaredifference (SSD), or other difference metrics.

After identifying a reference block of a PU in a P slice, motionestimation unit 122 may generate a reference index that indicates thereference picture in list 0 containing the reference block and a motionvector that indicates a spatial displacement between the PU and thereference block. In various examples, motion estimation unit 122 maygenerate motion vectors to varying degrees of precision. For example,motion estimation unit 122 may generate motion vectors at one-quartersample precision, one-eighth sample precision, or other fractionalsample precision. In the case of fractional sample precision, referenceblock values may be interpolated from integer-position sample values inthe reference picture. Motion estimation unit 122 may output thereference index and the motion vector as the motion information of thePU. Motion compensation unit 124 may generate a predicted video block ofthe PU based on the reference block identified by the motion informationof the PU.

If the PU is in a B slice, the picture containing the PU may beassociated with two lists of reference pictures, referred to as “list 0”and “list 1.” In some examples, a picture containing a B slice may beassociated with a list combination that is a combination of list 0 andlist 1.

Furthermore, if the PU is in a B slice, motion estimation unit 122 mayperform uni-directional prediction or bi-directional prediction for thePU. When motion estimation unit 122 performs uni-directional predictionfor the PU, motion estimation unit 122 may search the reference picturesof list 0 or list 1 for a reference block for the PU. Motion estimationunit 122 may then generate a reference index that indicates thereference picture in list 0 or list 1 that contains the reference blockand a motion vector that indicates a spatial displacement between the PUand the reference block. Motion estimation unit 122 may output thereference index, a prediction direction indicator, and the motion vectoras the motion information of the PU. The prediction direction indicatormay indicate whether the reference index indicates a reference picturein list 0 or list 1. Motion compensation unit 124 may generate thepredicted video block of the PU based on the reference block indicatedby the motion information of the PU.

When motion estimation unit 122 performs bi-directional prediction for aPU, motion estimation unit 122 may search the reference pictures in list0 for a reference block for the PU and may also search the referencepictures in list 1 for another reference block for the PU. Motionestimation unit 122 may then generate reference indexes that indicatethe reference pictures in list 0 and list 1 containing the referenceblocks and motion vectors that indicate spatial displacements betweenthe reference blocks and the PU. Motion estimation unit 122 may outputthe reference indexes and the motion vectors of the PU as the motioninformation of the PU. Motion compensation unit 124 may generate thepredicted video block of the PU based on the reference blocks indicatedby the motion information of the PU.

In some instances, motion estimation unit 122 does not output a full setof motion information for a PU to entropy encoding unit 116. Rather,motion estimation unit 122 may signal the motion information of a PUwith reference to the motion information of another PU. For example,motion estimation unit 122 may determine that the motion information ofthe PU is sufficiently similar to the motion information of aneighboring PU. In this example, motion estimation unit 122 mayindicate, in a syntax structure associated with the PU, a value thatindicates to the video decoder 30 that the PU has the same motioninformation as the neighboring PU. In another example, motion estimationunit 122 may identify, in a syntax structure associated with the PU, aneighboring PU and a motion vector difference (MVD). The motion vectordifference indicates a difference between the motion vector of the PUand the motion vector of the indicated neighboring PU. The video decoder30 may use the motion vector of the indicated neighboring PU and themotion vector difference to determine the motion vector of the PU. Byreferring to the motion information of a first PU when signaling themotion information of a second PU, the video encoder 20 may be able tosignal the motion information of the second PU using fewer bits.

As further discussed below with reference to FIGS. 8-9, the predictionprocessing unit 100 may be configured to code (e.g., encode or decode)the PU (or any other reference layer and/or enhancement layer blocks orvideo units) by performing the methods illustrated in FIGS. 8-9. Forexample, inter prediction unit 121 (e.g., via motion estimation unit 122and/or motion compensation unit 124), intra prediction unit 126, orinter-layer prediction unit 128 may be configured to perform the methodsillustrated in FIGS. 8-9, either together or separately.

As part of performing an encoding operation on a CU, intra predictionunit 126 may perform intra prediction on PUs of the CU. Intra predictionmay provide spatial compression. When intra prediction unit 126 performsintra prediction on a PU, intra prediction unit 126 may generateprediction data for the PU based on decoded samples of other PUs in thesame picture. The prediction data for the PU may include a predictedvideo block and various syntax elements. Intra prediction unit 126 mayperform intra prediction on PUs in I slices, P slices, and B slices.

To perform intra prediction on a PU, intra prediction unit 126 may usemultiple intra prediction modes to generate multiple sets of predictiondata for the PU. When intra prediction unit 126 uses an intra predictionmode to generate a set of prediction data for the PU, intra predictionunit 126 may extend samples from video blocks of neighboring PUs acrossthe video block of the PU in a direction and/or gradient associated withthe intra prediction mode. The neighboring PUs may be above, above andto the right, above and to the left, or to the left of the PU, assuminga left-to-right, top-to-bottom encoding order for PUs, CUs, andtreeblocks. Intra prediction unit 126 may use various numbers of intraprediction modes, e.g., 33 directional intra prediction modes, dependingon the size of the PU.

Prediction processing unit 100 may select the prediction data for a PUfrom among the prediction data generated by motion compensation unit 124for the PU or the prediction data generated by intra prediction unit 126for the PU. In some examples, prediction processing unit 100 selects theprediction data for the PU based on rate/distortion metrics of the setsof prediction data.

If prediction processing unit 100 selects prediction data generated byintra prediction unit 126, prediction processing unit 100 may signal theintra prediction mode that was used to generate the prediction data forthe PUs, e.g., the selected intra prediction mode. Prediction processingunit 100 may signal the selected intra prediction mode in various ways.For example, it may be probable that the selected intra prediction modeis the same as the intra prediction mode of a neighboring PU. In otherwords, the intra prediction mode of the neighboring PU may be the mostprobable mode for the current PU. Thus, prediction processing unit 100may generate a syntax element to indicate that the selected intraprediction mode is the same as the intra prediction mode of theneighboring PU.

As discussed above, the video encoder 20 may include inter-layerprediction unit 128. Inter-layer prediction unit 128 is configured topredict a current block (e.g., a current block in the EL) using one ormore different layers that are available in SVC (e.g., a base orreference layer). Such prediction may be referred to as inter-layerprediction. Inter-layer prediction unit 128 utilizes prediction methodsto reduce inter-layer redundancy, thereby improving coding efficiencyand reducing computational resource requirements. Some examples ofinter-layer prediction include inter-layer intra prediction, inter-layermotion prediction, and inter-layer residual prediction. Inter-layerintra prediction uses the reconstruction of co-located blocks in thebase layer to predict the current block in the enhancement layer.Inter-layer motion prediction uses motion information of the base layerto predict motion in the enhancement layer. Inter-layer residualprediction uses the residue of the base layer to predict the residue ofthe enhancement layer. Each of the inter-layer prediction schemes isdiscussed below in greater detail.

After prediction processing unit 100 selects the prediction data for PUsof a CU, residual generation unit 102 may generate residual data for theCU by subtracting (e.g., indicated by the minus sign) the predictedvideo blocks of the PUs of the CU from the video block of the CU. Theresidual data of a CU may include 2D residual video blocks thatcorrespond to different sample components of the samples in the videoblock of the CU. For example, the residual data may include a residualvideo block that corresponds to differences between luminance componentsof samples in the predicted video blocks of the PUs of the CU andluminance components of samples in the original video block of the CU.In addition, the residual data of the CU may include residual videoblocks that correspond to the differences between chrominance componentsof samples in the predicted video blocks of the PUs of the CU and thechrominance components of the samples in the original video block of theCU.

Prediction processing unit 100 may perform quadtree partitioning topartition the residual video blocks of a CU into sub-blocks. Eachundivided residual video block may be associated with a different TU ofthe CU. The sizes and positions of the residual video blocks associatedwith TUs of a CU may or may not be based on the sizes and positions ofvideo blocks associated with the PUs of the CU. A quadtree structureknown as a “residual quad tree” (RQT) may include nodes associated witheach of the residual video blocks. The TUs of a CU may correspond toleaf nodes of the RQT.

Transform processing unit 104 may generate one or more transformcoefficient blocks for each TU of a CU by applying one or moretransforms to a residual video block associated with the TU. Each of thetransform coefficient blocks may be a 2D matrix of transformcoefficients. Transform processing unit 104 may apply various transformsto the residual video block associated with a TU. For example, transformprocessing unit 104 may apply a discrete cosine transform (DCT), adirectional transform, or a conceptually similar transform to theresidual video block associated with a TU.

After transform processing unit 104 generates a transform coefficientblock associated with a TU, quantization unit 106 may quantize thetransform coefficients in the transform coefficient block. Quantizationunit 106 may quantize a transform coefficient block associated with a TUof a CU based on a QP value associated with the CU.

The video encoder 20 may associate a QP value with a CU in various ways.For example, the video encoder 20 may perform a rate-distortion analysison a treeblock associated with the CU. In the rate-distortion analysis,the video encoder 20 may generate multiple coded representations of thetreeblock by performing an encoding operation multiple times on thetreeblock. The video encoder 20 may associate different QP values withthe CU when the video encoder 20 generates different encodedrepresentations of the treeblock. The video encoder 20 may signal that agiven QP value is associated with the CU when the given QP value isassociated with the CU in a coded representation of the treeblock thathas a lowest bitrate and distortion metric.

Inverse quantization unit 108 and inverse transform unit 110 may applyinverse quantization and inverse transforms to the transform coefficientblock, respectively, to reconstruct a residual video block from thetransform coefficient block. Reconstruction unit 112 may add thereconstructed residual video block to corresponding samples from one ormore predicted video blocks generated by prediction processing unit 100to produce a reconstructed video block associated with a TU. Byreconstructing video blocks for each TU of a CU in this way, the videoencoder 20 may reconstruct the video block of the CU.

After reconstruction unit 112 reconstructs the video block of a CU,filter unit 113 may perform a deblocking operation to reduce blockingartifacts in the video block associated with the CU. After performingthe one or more deblocking operations, filter unit 113 may store thereconstructed video block of the CU in decoded picture buffer 114.Motion estimation unit 122 and motion compensation unit 124 may use areference picture that contains the reconstructed video block to performinter prediction on PUs of subsequent pictures. In addition, intraprediction unit 126 may use reconstructed video blocks in decodedpicture buffer 114 to perform intra prediction on other PUs in the samepicture as the CU.

Entropy encoding unit 116 may receive data from other functionalcomponents of the video encoder 20. For example, entropy encoding unit116 may receive transform coefficient blocks from quantization unit 106and may receive syntax elements from prediction processing unit 100.When entropy encoding unit 116 receives the data, entropy encoding unit116 may perform one or more entropy encoding operations to generateentropy encoded data. For example, the video encoder 20 may perform acontext adaptive variable length coding (CAVLC) operation, a CABACoperation, a variable-to-variable (V2V) length coding operation, asyntax-based context-adaptive binary arithmetic coding (SBAC) operation,a Probability Interval Partitioning Entropy (PIPE) coding operation, oranother type of entropy encoding operation on the data. Entropy encodingunit 116 may output a bitstream that includes the entropy encoded data.

As part of performing an entropy encoding operation on data, entropyencoding unit 116 may select a context model. If entropy encoding unit116 is performing a CABAC operation, the context model may indicateestimates of probabilities of particular bins having particular values.In the context of CABAC, the term “bin” is used to refer to a bit of abinarized version of a syntax element.

Multi-Layer Video Encoder

FIG. 2B is a block diagram illustrating an example of a multi-layervideo encoder 23 (also simply referred to as video encoder 23) that mayimplement techniques in accordance with aspects described in thisdisclosure. The video encoder 23 may be configured to processmulti-layer video frames, such as for SHVC and multiview coding.Further, the video encoder 23 may be configured to perform any or all ofthe techniques of this disclosure.

The video encoder 23 includes a video encoder 20A and video encoder 20B,each of which may be configured as the video encoder 20 and may performthe functions described above with respect to the video encoder 20.Further, as indicated by the reuse of reference numbers, the videoencoders 20A and 20B may include at least some of the systems andsubsystems as the video encoder 20. Although the video encoder 23 isillustrated as including two video encoders 20A and 20B, the videoencoder 23 is not limited as such and may include any number of videoencoder 20 layers. In some embodiments, the video encoder 23 may includea video encoder 20 for each picture or frame in an access unit. Forexample, an access unit that includes five pictures may be processed orencoded by a video encoder that includes five encoder layers. In someembodiments, the video encoder 23 may include more encoder layers thanframes in an access unit. In some such cases, some of the video encoderlayers may be inactive when processing some access units.

In addition to the video encoders 20A and 20B, the video encoder 23 mayinclude an resampling unit 90. The resampling unit 90 may, in somecases, upsample a base layer of a received video frame to, for example,create an enhancement layer. The resampling unit 90 may upsampleparticular information associated with the received base layer of aframe, but not other information. For example, the resampling unit 90may up sample the spatial size or number of pixels of the base layer,but the number of slices or the POC may remain constant. In some cases,the resampling unit 90 may not process the received video and/or may beoptional. For example, in some cases, the prediction processing unit 100may perform upsampling. In some embodiments, the resampling unit 90 isconfigured to upsample a layer and reorganize, redefine, modify, oradjust one or more slices to comply with a set of slice boundary rulesand/or raster scan rules. Although primarily described as upsampling abase layer, or a lower layer in an access unit, in some cases, theresampling unit 90 may downsample a layer. For example, if duringstreaming of a video bandwidth is reduced, a frame may be downsampledinstead of upsampled.

The resampling unit 90 may be configured to receive a picture or frame(or picture information associated with the picture) from the decodedpicture buffer 114 of the lower layer encoder (e.g., the video encoder20A) and to upsample the picture (or the received picture information).This upsampled picture may then be provided to the prediction processingunit 100 of a higher layer encoder (e.g., the video encoder 20B)configured to encode a picture in the same access unit as the lowerlayer encoder. In some cases, the higher layer encoder is one layerremoved from the lower layer encoder. In other cases, there may be oneor more higher layer encoders between the layer 0 video encoder and thelayer 1 encoder of FIG. 2B.

In some cases, the resampling unit 90 may be omitted or bypassed. Insuch cases, the picture from the decoded picture buffer 114 of the videoencoder 20A may be provided directly, or at least without being providedto the resampling unit 90, to the prediction processing unit 100 of thevideo encoder 20B. For example, if video data provided to the videoencoder 20B and the reference picture from the decoded picture buffer114 of the video encoder 20A are of the same size or resolution, thereference picture may be provided to the video encoder 20B without anyresampling.

In some embodiments, the video encoder 23 downsamples video data to beprovided to the lower layer encoder using the downsampling unit 94before provided the video data to the video encoder 20A. Alternatively,the downsampling unit 94 may be a resampling unit 90 capable ofupsampling or downsampling the video data. In yet other embodiments, thedownsampling unit 94 may be omitted.

As illustrated in FIG. 2B, the video encoder 23 may further include amultiplexor 98, or mux. The mux 98 can output a combined bitstream fromthe video encoder 23. The combined bitstream may be created by taking abitstream from each of the video encoders 20A and 20B and alternatingwhich bitstream is output at a given time. While in some cases the bitsfrom the two (or more in the case of more than two video encoder layers)bitstreams may be alternated one bit at a time, in many cases thebitstreams are combined differently. For example, the output bitstreammay be created by alternating the selected bitstream one block at atime. In another example, the output bitstream may be created byoutputting a non-1:1 ratio of blocks from each of the video encoders 20Aand 20B. For instance, two blocks may be output from the video encoder20B for each block output from the video encoder 20A. In someembodiments, the output stream from the mux 98 may be preprogrammed. Inother embodiments, the mux 98 may combine the bitstreams from the videoencoders 20A, 20B based on a control signal received from a systemexternal to the video encoder 23, such as from a processor on a sourcedevice including the source device 12. The control signal may begenerated based on the resolution or bitrate of a video from the videosource 18, based on a bandwidth of the link 16, based on a subscriptionassociated with a user (e.g., a paid subscription versus a freesubscription), or based on any other factor for determining a resolutionoutput desired from the video encoder 23.

Video Decoder

FIG. 3A is a block diagram illustrating an example of the video decoder30 that may implement techniques in accordance with aspects described inthis disclosure. The video decoder 30 may be configured to process asingle layer of a video frame, such as for HEVC. Further, the videodecoder 30 may be configured to perform any or all of the techniques ofthis disclosure, including but not limited to the methods of inferringNoOutputOfPriorPicsFlag and related processes described in greaterdetail above and below with respect to FIGS. 4 and 5. As one example,motion compensation unit 162 and/or intra prediction unit 164 may beconfigured to perform any or all of the techniques described in thisdisclosure. In one embodiment, the video decoder 30 may optionallyinclude inter-layer prediction unit 166 that is configured to performany or all of the techniques described in this disclosure. In otherembodiments, inter-layer prediction can be performed by predictionprocessing unit 152 (e.g., motion compensation unit 162 and/or intraprediction unit 164), in which case the inter-layer prediction unit 166may be omitted. However, aspects of this disclosure are not so limited.In some examples, the techniques described in this disclosure may beshared among the various components of the video decoder 30. In someexamples, additionally or alternatively, a processor (not shown) may beconfigured to perform any or all of the techniques described in thisdisclosure.

For purposes of explanation, this disclosure describes the video decoder30 in the context of HEVC coding. However, the techniques of thisdisclosure may be applicable to other coding standards or methods. Theexample depicted in FIG. 3A is for a single layer codec. However, aswill be described further with respect to FIG. 3B, some or all of thevideo decoder 30 may be duplicated for processing of a multi-layercodec.

In the example of FIG. 3A, the video decoder 30 includes a plurality offunctional components. The functional components of the video decoder 30include an entropy decoding unit 150, a prediction processing unit 152,an inverse quantization unit 154, an inverse transform unit 156, areconstruction unit 158, a filter unit 159, and a decoded picture buffer160. Prediction processing unit 152 includes a motion compensation unit162, an intra prediction unit 164, and an inter-layer prediction unit166. In some examples, the video decoder 30 may perform a decoding passgenerally reciprocal to the encoding pass described with respect to thevideo encoder 20 of FIG. 2A. In other examples, the video decoder 30 mayinclude more, fewer, or different functional components.

The video decoder 30 may receive a bitstream that comprises encodedvideo data. The bitstream may include a plurality of syntax elements.When the video decoder 30 receives the bitstream, entropy decoding unit150 may perform a parsing operation on the bitstream. As a result ofperforming the parsing operation on the bitstream, entropy decoding unit150 may extract syntax elements from the bitstream. As part ofperforming the parsing operation, entropy decoding unit 150 may entropydecode entropy encoded syntax elements in the bitstream. Predictionprocessing unit 152, inverse quantization unit 154, inverse transformunit 156, reconstruction unit 158, and filter unit 159 may perform areconstruction operation that generates decoded video data based on thesyntax elements extracted from the bitstream.

As discussed above, the bitstream may comprise a series of NAL units.The NAL units of the bitstream may include video parameter set NALunits, sequence parameter set NAL units, picture parameter set NALunits, SEI NAL units, and so on. As part of performing the parsingoperation on the bitstream, entropy decoding unit 150 may performparsing operations that extract and entropy decode sequence parametersets from sequence parameter set NAL units, picture parameter sets frompicture parameter set NAL units, SEI data from SEI NAL units, and so on.

In addition, the NAL units of the bitstream may include coded slice NALunits. As part of performing the parsing operation on the bitstream,entropy decoding unit 150 may perform parsing operations that extractand entropy decode coded slices from the coded slice NAL units. Each ofthe coded slices may include a slice header and slice data. The sliceheader may contain syntax elements pertaining to a slice. The syntaxelements in the slice header may include a syntax element thatidentifies a picture parameter set associated with a picture thatcontains the slice. Entropy decoding unit 150 may perform entropydecoding operations, such as CABAC decoding operations, on syntaxelements in the coded slice header to recover the slice header.

As part of extracting the slice data from coded slice NAL units, entropydecoding unit 150 may perform parsing operations that extract syntaxelements from coded CUs in the slice data. The extracted syntax elementsmay include syntax elements associated with transform coefficientblocks. Entropy decoding unit 150 may then perform CABAC decodingoperations on some of the syntax elements.

After entropy decoding unit 150 performs a parsing operation on anon-partitioned CU, the video decoder 30 may perform a reconstructionoperation on the non-partitioned CU. To perform the reconstructionoperation on a non-partitioned CU, the video decoder 30 may perform areconstruction operation on each TU of the CU. By performing thereconstruction operation for each TU of the CU, the video decoder 30 mayreconstruct a residual video block associated with the CU.

As part of performing a reconstruction operation on a TU, inversequantization unit 154 may inverse quantize, e.g., de-quantize, atransform coefficient block associated with the TU. Inverse quantizationunit 154 may inverse quantize the transform coefficient block in amanner similar to the inverse quantization processes proposed for HEVCor defined by the H.264 decoding standard. Inverse quantization unit 154may use a quantization parameter QP calculated by the video encoder 20for a CU of the transform coefficient block to determine a degree ofquantization and, likewise, a degree of inverse quantization for inversequantization unit 154 to apply.

After inverse quantization unit 154 inverse quantizes a transformcoefficient block, inverse transform unit 156 may generate a residualvideo block for the TU associated with the transform coefficient block.Inverse transform unit 156 may apply an inverse transform to thetransform coefficient block in order to generate the residual videoblock for the TU. For example, inverse transform unit 156 may apply aninverse DCT, an inverse integer transform, an inverse Karhunen-Loevetransform (KLT), an inverse rotational transform, an inverse directionaltransform, or another inverse transform to the transform coefficientblock. In some examples, inverse transform unit 156 may determine aninverse transform to apply to the transform coefficient block based onsignaling from the video encoder 20. In such examples, inverse transformunit 156 may determine the inverse transform based on a signaledtransform at the root node of a quadtree for a treeblock associated withthe transform coefficient block. In other examples, inverse transformunit 156 may infer the inverse transform from one or more codingcharacteristics, such as block size, coding mode, or the like. In someexamples, inverse transform unit 156 may apply a cascaded inversetransform.

In some examples, motion compensation unit 162 may refine the predictedvideo block of a PU by performing interpolation based on interpolationfilters. Identifiers for interpolation filters to be used for motioncompensation with sub-sample precision may be included in the syntaxelements. Motion compensation unit 162 may use the same interpolationfilters used by the video encoder 20 during generation of the predictedvideo block of the PU to calculate interpolated values for sub-integersamples of a reference block. Motion compensation unit 162 may determinethe interpolation filters used by the video encoder 20 according toreceived syntax information and use the interpolation filters to producethe predicted video block.

As further discussed below with reference to FIGS. 8-9, the predictionprocessing unit 152 may code (e.g., encode or decode) the PU (or anyother reference layer and/or enhancement layer blocks or video units) byperforming the methods illustrated in FIGS. 8-9. For example, motioncompensation unit 162, intra prediction unit 164, or inter-layerprediction unit 166 may be configured to perform the methods illustratedin FIGS. 8-9, either together or separately.

If a PU is encoded using intra prediction, intra prediction unit 164 mayperform intra prediction to generate a predicted video block for the PU.For example, intra prediction unit 164 may determine an intra predictionmode for the PU based on syntax elements in the bitstream. The bitstreammay include syntax elements that intra prediction unit 164 may use todetermine the intra prediction mode of the PU.

In some instances, the syntax elements may indicate that intraprediction unit 164 is to use the intra prediction mode of another PU todetermine the intra prediction mode of the current PU. For example, itmay be probable that the intra prediction mode of the current PU is thesame as the intra prediction mode of a neighboring PU. In other words,the intra prediction mode of the neighboring PU may be the most probablemode for the current PU. Hence, in this example, the bitstream mayinclude a small syntax element that indicates that the intra predictionmode of the PU is the same as the intra prediction mode of theneighboring PU. Intra prediction unit 164 may then use the intraprediction mode to generate prediction data (e.g., predicted samples)for the PU based on the video blocks of spatially neighboring PUs.

As discussed above, the video decoder 30 may also include inter-layerprediction unit 166. Inter-layer prediction unit 166 is configured topredict a current block (e.g., a current block in the EL) using one ormore different layers that are available in SVC (e.g., a base orreference layer). Such prediction may be referred to as inter-layerprediction. Inter-layer prediction unit 166 utilizes prediction methodsto reduce inter-layer redundancy, thereby improving coding efficiencyand reducing computational resource requirements. Some examples ofinter-layer prediction include inter-layer intra prediction, inter-layermotion prediction, and inter-layer residual prediction. Inter-layerintra prediction uses the reconstruction of co-located blocks in thebase layer to predict the current block in the enhancement layer.Inter-layer motion prediction uses motion information of the base layerto predict motion in the enhancement layer. Inter-layer residualprediction uses the residue of the base layer to predict the residue ofthe enhancement layer. Each of the inter-layer prediction schemes isdiscussed below in greater detail.

Reconstruction unit 158 may use the residual video blocks associatedwith TUs of a CU and the predicted video blocks of the PUs of the CU,e.g., either intra-prediction data or inter-prediction data, asapplicable, to reconstruct the video block of the CU. Thus, the videodecoder 30 may generate a predicted video block and a residual videoblock based on syntax elements in the bitstream and may generate a videoblock based on the predicted video block and the residual video block.

After reconstruction unit 158 reconstructs the video block of the CU,filter unit 159 may perform a deblocking operation to reduce blockingartifacts associated with the CU. After filter unit 159 performs adeblocking operation to reduce blocking artifacts associated with theCU, the video decoder 30 may store the video block of the CU in decodedpicture buffer 160. Decoded picture buffer 160 may provide referencepictures for subsequent motion compensation, intra prediction, andpresentation on a display device, such as display device 32 of FIG. 1Aor 1B. For instance, the video decoder 30 may perform, based on thevideo blocks in decoded picture buffer 160, intra prediction or interprediction operations on PUs of other CUs.

Multi-Layer Decoder

FIG. 3B is a block diagram illustrating an example of a multi-layervideo decoder 33 (also simply referred to as video decoder 33) that mayimplement techniques in accordance with aspects described in thisdisclosure. The video decoder 33 may be configured to processmulti-layer video frames, such as for SHVC and multiview coding.Further, the video decoder 33 may be configured to perform any or all ofthe techniques of this disclosure.

The video decoder 33 includes a video decoder 30A and video decoder 30B,each of which may be configured as the video decoder 30 and may performthe functions described above with respect to the video decoder 30.Further, as indicated by the reuse of reference numbers, the videodecoders 30A and 30B may include at least some of the systems andsubsystems as the video decoder 30. Although the video decoder 33 isillustrated as including two video decoders 30A and 30B, the videodecoder 33 is not limited as such and may include any number of videodecoder 30 layers. In some embodiments, the video decoder 33 may includea video decoder 30 for each picture or frame in an access unit. Forexample, an access unit that includes five pictures may be processed ordecoded by a video decoder that includes five decoder layers. In someembodiments, the video decoder 33 may include more decoder layers thanframes in an access unit. In some such cases, some of the video decoderlayers may be inactive when processing some access units.

In addition to the video decoders 30A and 30B, the video decoder 33 mayinclude an upsampling unit 92. In some embodiments, the upsampling unit92 may upsample a base layer of a received video frame to create anenhanced layer to be added to the reference picture list for the frameor access unit. This enhanced layer can be stored in the decoded picturebuffer 160. In some embodiments, the upsampling unit 92 can include someor all of the embodiments described with respect to the resampling unit90 of FIG. 2A. In some embodiments, the upsampling unit 92 is configuredto upsample a layer and reorganize, redefine, modify, or adjust one ormore slices to comply with a set of slice boundary rules and/or rasterscan rules. In some cases, the upsampling unit 92 may be a resamplingunit configured to upsample and/or downsample a layer of a receivedvideo frame

The upsampling unit 92 may be configured to receive a picture or frame(or picture information associated with the picture) from the decodedpicture buffer 160 of the lower layer decoder (e.g., the video decoder30A) and to upsample the picture (or the received picture information).This upsampled picture may then be provided to the prediction processingunit 152 of a higher layer decoder (e.g., the video decoder 30B)configured to decode a picture in the same access unit as the lowerlayer decoder. In some cases, the higher layer decoder is one layerremoved from the lower layer decoder. In other cases, there may be oneor more higher layer decoders between the layer 0 decoder and the layer1 decoder of FIG. 3B.

In some cases, the upsampling unit 92 may be omitted or bypassed. Insuch cases, the picture from the decoded picture buffer 160 of the videodecoder 30A may be provided directly, or at least without being providedto the upsampling unit 92, to the prediction processing unit 152 of thevideo decoder 30B. For example, if video data provided to the videodecoder 30B and the reference picture from the decoded picture buffer160 of the video decoder 30A are of the same size or resolution, thereference picture may be provided to the video decoder 30B withoutupsampling. Further, in some embodiments, the upsampling unit 92 may bea resampling unit 90 configured to upsample or downsample a referencepicture received from the decoded picture buffer 160 of the videodecoder 30A.

As illustrated in FIG. 3B, the video decoder 33 may further include ademultiplexor 99, or demux. The demux 99 can split an encoded videobitstream into multiple bitstreams with each bitstream output by thedemux 99 being provided to a different video decoder 30A and 30B. Themultiple bitstreams may be created by receiving a bitstream and each ofthe video decoders 30A and 30B receives a portion of the bitstream at agiven time. While in some cases the bits from the bitstream received atthe demux 99 may be alternated one bit at a time between each of thevideo decoders (e.g., video decoders 30A and 30B in the example of FIG.3B), in many cases the bitstream is divided differently. For example,the bitstream may be divided by alternating which video decoder receivesthe bitstream one block at a time. In another example, the bitstream maybe divided by a non-1:1 ratio of blocks to each of the video decoders30A and 30B. For instance, two blocks may be provided to the videodecoder 30B for each block provided to the video decoder 30A. In someembodiments, the division of the bitstream by the demux 99 may bepreprogrammed. In other embodiments, the demux 99 may divide thebitstream based on a control signal received from a system external tothe video decoder 33, such as from a processor on a destination deviceincluding the destination device 14. The control signal may be generatedbased on the resolution or bitrate of a video from the input interface28, based on a bandwidth of the link 16, based on a subscriptionassociated with a user (e.g., a paid subscription versus a freesubscription), or based on any other factor for determining a resolutionobtainable by the video decoder 33.

Intra Random Access Point (IRAP) Pictures

Some video coding schemes may provide various random access pointsthroughout the bitstream such that the bitstream may be decoded startingfrom any of those random access points without needing to decode anypictures that precede those random access points in the bitstream. Insuch video coding schemes, pictures that follow a random access point inoutput order (e.g., including those pictures that are in the same accessunit as the picture providing the random access point) can be correctlydecoded without using any pictures that precede the random access point.For example, even if a portion of the bitstream is lost duringtransmission or during decoding, a decoder can resume decoding thebitstream starting from the next random access point. Support for randomaccess may facilitate, for example, dynamic streaming services, seekoperations, channel switching, etc. In some cases, pictures that followa random access point in output order may use leading pictures fordecoding. Leading pictures may refer to pictures that follow the randomaccess point in the bitstream and are output and displayed before therandom access point.

In some coding schemes, such random access points may be provided bypictures that are referred to as IRAP pictures. For example, a randomaccess point (e.g., provided by an enhancement layer IRAP picture) in anenhancement layer (“layerA”) contained in an access unit (“auA”) mayprovide layer-specific random access such that for each reference layer(“layerB”) of layerA (e.g., a reference layer being a layer that is usedto predict layerA) having a random access point contained in an accessunit (“auB”) that is in layerB and precedes auA in decoding order (or arandom access point contained in auA), the pictures in layerA thatfollow auB in output order (including those pictures located in auB),may be correctly decodable without needing to decode any pictures inlayerA that precede auB. For example, when decoding starts from auB, anda picture in layerB and in auB is decodable, then the picture in layer Athat is in auA and pictures in layerA that follow auA are decodable.

IRAP pictures may be coded using intra prediction (e.g., coded withoutreferring to other pictures in the same layer), and may include, forexample, instantaneous decoding refresh (IDR) pictures, clean randomaccess (CRA) pictures, and broken link access (BLA) pictures. When thereis an IDR picture in the bitstream, the pictures that precede the IDRpicture in decoding order are not used for prediction by pictures thatfollow the IDR picture in decoding order. When there is a CRA picture inthe bitstream, the pictures that follow the CRA picture may or may notuse pictures that precede the CRA picture in decoding order forprediction. Those pictures that follow the CRA picture in decoding orderbut use pictures that precede the CRA picture in decoding order may bereferred to as random access skipped leading (RASL) pictures. Anothertype of picture that follows an IRAP picture in decoding order andprecedes the IRAP picture in output order is a random access decodableleading (RADL) picture, which may not contain references to any picturesthat precede the IRAP picture in decoding order. RASL pictures may bediscarded by the decoder if the pictures that precede the CRA pictureare not available. RASL pictures may or may not be present after a BLApicture. When RASL pictures are present after BLA pictures, they shouldbe ignored and/or not decoded because their reference pictures may notbe available. An access unit (e.g., a group of pictures including thecoded pictures associated with the same output time across multiplelayers) containing a base layer picture (e.g., a picture having a layerID value of 0) that is an IRAP picture may be referred to as an IRAPaccess unit.

Cross-Layer Alignment of IRAP Pictures

In HEVC extensions such as SHVC and MV-HEVC, IRAP pictures may not berequired to be aligned (e.g., contained in the same access unit) acrossdifferent layers. For example, if IRAP pictures were required to bealigned, any access unit containing at least one IRAP picture would onlycontain IRAP pictures. On the other hand, if IRAP pictures were notrequired to be aligned, in a single access unit, one picture (e.g., in afirst layer) may be an IRAP picture, and another picture (e.g., in asecond layer) may be a non-IRAP picture. Having such non-aligned IRAPpictures in a bitstream may provide some advantages. For example, in atwo-layer bitstream, if there are more IRAP pictures in the base layerthan in the enhancement layer, in broadcast and multicast applications,low tune-in delay and high coding efficiency can be achieved.

In some video coding schemes, a POC may be used to keep track of therelative order in which the decoded pictures are displayed. Some of suchcoding schemes may cause the POC values to be reset (e.g., set to zeroor set to some value signaled in the bitstream) whenever certain typesof pictures appear in the bitstream. For example, the POC values ofcertain IRAP pictures may be reset, causing the POC values of otherpictures preceding those IRAP pictures in decoding order to also bereset. This may be problematic when the IRAP pictures are not requiredto be aligned across different layers. For example, when one picture(“picA”) is an IRAP picture and another picture (“picB”) in the sameaccess unit is not an IRAP picture, the POC value of a picture (“picC”),which is reset due to picA being an IRAP picture, in the layercontaining picA may be different from the POC value of a picture(“picD”), which is not reset, in the layer containing picB, where picCand picD are in the same access unit. This causes picC and picD to havedifferent POC values even though they belong to the same access unit(e.g., same output time). Thus, in this example, the derivation processfor deriving the POC values of picC and picD can be modified to producePOC values that are consistent with the definition of POC values andaccess units.

Resetting POC for Multi-Layer Coding

The poc_reset_idc syntax element may indicate whether the POC should bereset for a picture. The poc_reset_idc syntax element can indicatewhether the MSB of the POC should be reset, or both the MSB and the LSBof the POC should be reset, or none should be reset. For example, thevalue of 0 for the poc_reset_idc indicates that the POC is not reset.The value of 1 for the poc_reset_idc indicates that the POC MSB shouldbe reset. The value of 2 for the poc_reset_idc indicates that both thePOC MSB and LSB should be reset. The value of 3 for the poc_reset_idcindicates that reset was indicated for a previous picture. For example,the value of poc_reset_idc for the previous picture was either 1 or 2.The value of 3 for poc_reset_idc may be used such that when the pictureat which the POC should be reset is lost (e.g., during the decodingprocess), the POC can be properly reset at subsequent pictures.

The full_poc_reset_flag can indicate whether the reset for the previouspicture was only for the POC MSB, or for both the POC MSB and LSB. Forinstance, the value of 0 for the full_poc_reset_flag indicates that onlythe MSB should be reset. The value of 1 for the full_poc_reset_flagindicates that both the MSB and LSB should be reset. Thefull_poc_reset_flag flag can be used in connection with poc_reset_idc.For example, when the value of poc_reset_idc is 3, thefull_poc_reset_flag can indicate whether the POC reset for the previouspicture was for only the MSB or for both the MSB and LSB.

In early versions of SHVC and MV-HEVC (e.g., SHVC Working Draft 6,MV-HEVC Working Draft 8, etc.), certain constraints or restrictionsapply, e.g., with respect to poc_reset_idc. However, these constraintsdo not properly reset the POC when a picture is not present or when apicture is discardable. Certain details relating to these restrictionsand issues associated with such restrictions are discussed in furtherdetail below, for example, in sections describing Missing or AbsentPictures, Discardable Pictures, and Mixing of BLA and CRA Pictures.

In addition, in the early versions of SHVC and MV-HEVC, there are norestrictions on the value of full_poc_reset_flag of a picture based onpoc_reset_idc of the POC resetting AU in the same POC resetting period.An incorrect value of full_poc_reset_flag may result in the POC resetmechanism not working properly. Certain details relating tofull_poc_reset_flag are discussed in further detail below, for example,in the section describing the full_poc_reset_flag.

In order to address these and other challenges, the techniques accordingto certain aspects reset the POC when a picture is not present (e.g.,missing or absent) or when a picture is discardable. The techniques alsoimpose a restriction on the value of full_poc_reset_flag of a picturebased on the value of poc_reset_idc. In this way, the techniques canmake sure that the POC is reset correctly. For example, the POC can bereset correctly when the picture with poc_reset_idc equal to either 1 or2 is missing. Certain details relating to POC reset are explainedfurther below.

Missing or Absent Pictures

Some constraints related to the value of poc_reset_idc may be asfollows. It may be a requirement of bitstream conformance that thefollowing constraints apply:

-   -   The value of poc_reset_idc shall not be equal to 1 or 2 for a        random access skipped leading (RASL) picture, a random access        decodable leading (RADL) picture, a sub-layer non-reference        picture, or a picture that has TemporalId greater than 0, or a        picture that has discardable_flag equal to 1. TemporalID can        indicate the ID of a temporal sub-layer of a layer.    -   The value of poc_reset_idc of all pictures in an AU shall be the        same.    -   When the picture in an AU with nuh_layer_id equal to 0 is an        intra random access point (IRAP) picture with a particular value        of nal_unit_type and there is at least one other picture in the        same AU with a different value of nal_unit_type, the value of        poc_reset_idc shall be equal to 1 or 2 for all pictures in the        AU.    -   When there is at least one picture (i) that has nuh_layer_id        greater than 0 and (ii) that is an instantaneous decoder refresh        (IDR) picture with a particular value of nal_unit_type in an AU        and (iii) there is at least one other picture in the same AU        with a different value of nal_unit_type, then the value of        poc_reset_idc shall be equal to 1 or 2 for all pictures in the        AU.    -   The value of poc_reset_idc of a clean random access (CRA) or        broken link access (BLA) picture shall be less than 3.    -   When the picture with nuh_layer_id equal to 0 in an AU is an IDR        picture and there is at least one non-IDR picture in the same        AU, the value of poc_reset_idc shall be equal to 2 for all        pictures in the AU.    -   When the picture with nuh_layer_id equal to 0 in an AU is not an        IDR picture, the value of poc_reset_idc shall not be equal to 2        for any picture in the AU.

Of the above-listed constraints, the case where an AU that has picturesnot present for some of the layers and that has one IRAP picture in atleast one layer is not covered. For example, an AU (e.g., AU D) containsan IDR picture in the base layer (BL), but contains no picture in theenhancement layer (EL). A case where a layer does not have a picture inan AU may be described as the AU having a missing picture, an absentpicture, a non-present picture, etc. The layer may not include a picturein this particular AU, or the picture may have been lost (e.g., duringthe decoding process). In such a situation, the POC should be resetbecause the POC of the IDR picture in the BL must be equal to 0.However, the POC chain in the enhancement layer continues. Failing toreset the POC of the enhancement layer pictures at AU D could result ina derived POC that is not cross-layer aligned for pictures in thesubsequent AU. However, none of the above-listed restrictions for thevalue of poc_reset_idc are applicable for this situation, and therefore,the POC reset is not mandated for AU D.

In another example, an AU (e.g. AU D) contains an IDR picture in the EL,but contains no picture in the BL. Similarly, in such a situation, thePOC should be reset because the POC MSB of the IDR picture in the ELwill be reset to 0. However, with existing approaches, POC reset is notmandated for AU D.

To ensure correct behavior, the POC reset may be required in AU D forboth cases described above. Furthermore, one or more pictures and/or AUthat immediately follow AU D should have poc_reset_idc equal to 3. Withthese changes, the POC reset may be conducted for the layer where thepicture was absent as soon as there is a picture in that layer.

There may be cases where the POC does not have to be reset for an AUcontaining an IRAP picture and also missing pictures. FIG. 4 illustratesexamples of such cases. AU A does not need to reset the POC since themissing pictures are from Layer 2 and there are no pictures in thatlayer until AU B that does reset the POC. AU B needs to reset POCbecause the second AU after AU B has a picture in Layer 2, unless thatsecond AU itself does the POC reset (here, it is assumed that the secondAU does not). AU C needs to reset POC because it has an IDR in Layer 0but non-IRAP(s) in other layers. AU D does not need to reset the POCbecause the AU has a cross-layer aligned IDR and no missing picture.Finally, AU E needs to reset the POC because the second AU after AU Ehas a picture in Layer 2, unless that second AU itself does the POCreset (again, it is assumed that the second AU does not).

Discardable Pictures

The above-described problem for missing pictures may similarly apply todiscardable pictures, which after being discarded would become absentpictures.

When IRAP pictures are cross-layer aligned, the POC reset is notrequired with existing approaches. However, there is no restriction thatprohibits an IRAP picture from being marked as a discardable picture.When an AU auA contains cross-layer aligned IRAP pictures and at leastone of the IRAP pictures is discardable, derivation of POC for thepictures in the subsequent Ails, in decoding order, may be incorrect ifthe discardable IRAP picture in the auA was removed as illustrated inthe example of FIG. 5. When the EL IDR picture in AU E is discarded, thevalue of POC most significant bit (MSB) of the EL picture in AU F may bederived to be equal to the value of POC MSB of the previous anchorpicture (e.g., 256). This can result in different POC values derived forpictures in the BL and the EL for AU F.

Mixing of BLA and CRA Pictures

With existing approaches, when a picture in an AU has nuh_layer_id equalto 0 and is an IRAP picture with a particular value of nal_unit_type,and there is at least one other picture in the same access unit with adifferent value of nal_unit_type, the value of poc_reset_idc is setequal to 1 or 2 for all pictures in the AU. This means that if an AU ina 2-layer bitstream contains a CRA picture in the BL and a BLA picturein the enhancement layer, then the POC reset, either resetting the POCMSB only or resetting both the POC MSB and least significant bit (LSB),is required. Such a constraint is not ideal, particularly for certainuse-cases.

FIG. 6 illustrates a layer switch-down and switch-up example in whichthe layer switch-up is conducted at the AU that contains cross-layeraligned CRA pictures, auA. As it is not required to do the POC resetwhen the nal_unit_type values of IRAP are cross-layer aligned, anencoder may not signal any POC reset information (e.g., poc_reset_idc,poc_reset_period_id, etc) in the slice segment header extension in theCRA pictures of the auA. However, for the layer switch-up, the systemmay change the NAL unit_type of the EL picture of the auA from CRA toBLA. In such a case, the constraint implies that, in addition tochanging the NAL unit type, a system entity that performs the switch-upoperation also needs to modify the slice segment header extension of thepictures in the auA to insert POC reset information. Such an additionalburden imposed on the system entity is unnecessary because the POC resetis not really needed in the illustrated situation. This appliessimilarly for splicing bitstreams at cross-layer aligned CRA pictureswhere only the base layer CRA picture is changed to be a BLA picture.

full_poc_reset_flag

When poc_reset_idc is equal to 3, full_poc_reset_flag is signaled toindicate whether both the POC MSB and LSB should be reset or whetheronly the POC MSB should be reset. The value of full_poc_reset_flag canindicate the value of poc_reset_idc of the first access unit in the samePOC resetting period. In some embodiments, a POC resetting period canrefer to a sequence of access units in decoding order, starting with anaccess unit with poc_reset_idc equal to 1 or 2 and a particular value ofpoc_reset_period_id and including all access units that either have thesame value of poc_reset_period_id or have poc_reset_idc equal to 0. Ifthe wrong value of the full_poc_reset_flag is signalled, the decodercould decrement the POC of earlier pictures by the wrong value. FIG. 7,provided below, illustrates an example where the encoder assigns anincorrect value for full_poc_reset_flag. Since the value ofpoc_reset_idc of the picture in AU E is 2, which means that both the POCMSB and LSB are reset, the value of full_poc_reset_flag (when present,in the pictures that succeed, in decoding order, AU E and that belong tothe same POC resetting period as AU E) must be 1 to guarantee that thecorrect value of DeltaPocVal is derived to decrement the value of POC ofearlier pictures. Since the value of full_poc_reset_flag is incorrectlysignaled as 0 for the Layer 1 picture in AU G, the value used todecrement the POC of pictures of Layer 1 (that precede, in decodingorder, AU E) is 64 instead of 102. The incorrect POC values of earlierpictures may affect the reference picture selection (RPS) derivationprocess as the decoder cannot find the correct reference pictures forthe current picture. In the illustrated example of FIG. 7, during theRPS derivation of the Layer 1 picture of AU G, the decoder cannot findreference pictures with POC equal to −1 and −2, and hence thesereference pictures are marked “unavailable for reference”.

Resetting POC and Setting Value of full_poc_reset_flag

To overcome the above-described issues with existing approaches for POCreset in multi-layer codecs, this disclosure describes improvementsbelow. In this disclosure, the following described techniques andapproaches may be used solely or in any combination.

In accordance with one or more aspects of the POC reset techniquesdescribed herein, there is provided an update of constraints related tothe value of poc_reset_idc. As such, if there is at least one missingpicture in the AU auA that contains an IRAP picture at the BL or an IDRpicture in an EL, then the value of poc_reset_idc should be equal to 1or 2 for all pictures in the AU.

For example, one way to detect a missing picture for the AU auA is asfollows: when the number of picture(s) in the AU auA is less than thenumber of pictures in the bitstream, then the AU auA may be indicated orpresumed as having missing pictures.

In another example, the value of poc_reset_idc is constrained to beequal to 1 or 2 when there is at least one missing picture in the layerlayerIdA of the AU auA that contains an IRAP picture at a BL or an IDRpicture in an EL and there is another AU auB that satisfies at least oneof the following:

-   -   belongs to a different POC resetting period than the access unit        auA;    -   has an IRAP picture with nuh_layer_id equal to 0 and        NoClrasOutputFlag equal to 1; or    -   is the last access unit in the bitstream in decoding order        and there is a picture with nuh_layer_id equal to layerIdA that        follows auA in decoding order and precedes the AU auB in        decoding order.

In another example, when there is no picture with nuh_layer equal to anyparticular value of nuh_layer_id layerIdA in the access unit auA, andthere is a picture picA with nuh_layer_id equal to layerIdA that followsauA in decoding order and the following condition is true, then the AUauA may be indicated or presumed as having missing pictures:

-   -   Let auB be the first AU that follows auA in decoding order and        belongs to a different POC resetting period than the access unit        auA, when present. Let auC be the first access unit that follows        auA in decoding order and has an IRAP picture with nuh_layer_id        equal to 0 and NoClrasOutputFlag equal to 1, when present. Let        auD be the first access unit that follows auA in decoding order        and has an IRAP picture in each of the layers in the bitstream,        when present. Either none of auB, auC, and auD exists in the        bitstream, or the picture picA precedes, in decoding order, the        first of auB (when present), auC (when present), and auD (when        present) in decoding order.

In accordance with one or more aspects of the POC reset techniquesdescribed herein, there is provided an update of constraints related tothe value of poc_reset_idc. As such, when there is at least onediscardable picture in the AU that contains IRAP picture at the BL or anIDR picture in an EL, then the value of poc_reset_idc should be equal to1 or 2 for all pictures in the AU.

In another example, a constraint may be added such that the IRAPpictures cannot have discardable_flag equal to 1.

In yet another example, a constraint may be added such that the IDRpictures are disallowed to have discardable_flag equal to 1 but CRA andBLA pictures are allowed to have discardable_flag equal to 1.

In accordance with one or more aspects of the POC reset techniquesdescribed herein, a constraint may be added for poc_reset_idc to ensurethat, when there is a missing picture or discardable picture of a layerlayerA in an access unit auA that contains an IRAP picture at the BL oran IDR picture in an EL, starting from the first AU following auA, indecoding order, that has picture with nuh_layer_id equal to layerA untilthe first AU that follows auA, in decoding order, containing picturewith nuh_layer_id equal to layerA that has TemporalId equal to 0 and hasdiscardable_flag equal to 0, inclusive, the value of poc_reset_idcshould be equal to 3.

In another example, poc_reset_idc should be equal to 3 for pictures oflayer layerA contained in access units that follow, in decoding order,auA and precede, in decoding order, the first AU that follows auA, indecoding order, containing a picture with nuh_layer_id equal to layerAthat has TemporalId equal to 0, has discardable_flag equal to 0 and isnot a RASL, RADL or sub-layer non-reference picture, inclusive. Asub-layer non-reference picture (SLNR) may refer to a picture that isnot used a reference picture by a temporal sublayer. For instance, alayer can consist of one or more temporal sub-layers that are indicatedby a temporal ID (e.g., TemporalId). If a picture that is in the highestlayer and that is at the highest temporal sub-layer is not used as areference by other pictures in the same layer, it may be removed withoutcausing the bitstream to become undecodable. In such case, the picturecan be similar to a discardable picture.

In accordance with one or more aspects of the POC reset techniquesdescribed herein, a constraint may be added to ensure that the value offull_poc_reset_flag of a picture indicates the correct value ofpoc_reset_idc of the first AU in the same POC resetting period as thecurrent picture.

In accordance with one or more aspects of the POC reset techniquesdescribed herein, an existing constraint for poc_reset_idc may bemodified to ensure that when an AU contains only CRA or BLA pictures(but with any type of BLA picture), POC resetting is not required (e.g.,poc_reset_idc is not required to be equal to 1 or 2).

EXEMPLARY EMBODIMENTS

The above mentioned techniques can be implemented as shown in thefollowing examples. The examples are provided in the context of earlierversions of SHVC and MV-HEVC (e.g., SHVC WD 6 and MV-HEVC WD 8).Additions to the earlier versions of SHVC and MV-HEVC are indicated initalics, and deletions from the earlier versions of SHVC and MV-HEVC areindicated in strikethrough.

Exemplary Embodiment 1

Embodiment 1 resets the POC when there is an absent picture or adiscardable picture in an AU. For example, a variable calledabsentPictureInAuFlag can indicate whether an AU contains an absentpicture or a discardable picture. If the first AU in the same POCresetting period has an absent picture or a discardable picture in aparticular layer, the value of poc_reset_idc is set to 3 for subsequentAUs in decoding order, starting with an AU that has a picture in thesame layer and ending with an AU that has a picture that is in the samelayer, has a temporal ID equal to 0, and is not discardable, inclusive.In addition, the value of full_poc_reset_flag can be set to the value ofpoc_reset_idc minus 1 when the value of poc_reset_idc of pictures in thefirst AU in the same POC resetting period is equal to 1 or 2.

For example, encoders should be cautious in setting the value ofpoc_reset_idc of pictures when there is a picture of a layer not presentin an AU or there is a picture with discardable_flag equal to 1 presentin an AU, to ensure that the derived POC values of pictures within an AUare cross-layer aligned. In some embodiments, such cases should betreated similarly as AUs with non-cross-layer-aligned IRAP pictures interms of whether the POC should be reset.

TABLE 1 Exemplary Embodiment 1 The variable absentPictureInAuFlag isderived as follows:     If any of the two following conditions is true,the value of absentPictureInAuFlag is set to be 1:         There is atleast one picture in the same access unit that has discardable_flagequal to 1.         The number of pictures in the access unit is lessthe number of layers in the bitstream.     Otherwise, the value ofabsentPictureInAuFlag is set to be 0. It is a requirement of bitstreamconformance that the following constraints apply:   The value ofpoc_reset_idc shall not be equal to 1 or 2 for a RASL picture, a RADLpicture, a sub-   layer non-reference picture, or a picture that hasTemporalId greater than 0, or a picture that has   discardable_flagequal to 1.   The value of poc_reset_idc of all pictures in an accessunit shall be the same.   When the picture in an access unit withnuh_layer_id equal to 0 is an IRAP picture 

  

 and there is at least one other picture in the same access unit that isnot an   IRAP picture or absentPictureInAuFlag is equal to 1  

 the   value of poc_reset_idc shall be equal to 1 or 2 for all picturesin the access unit.   When there is at least one picture that hasnuh_layer_id greater than 0 and that is an IDR picture with   aparticular value of nal_unit_type in an access unit and there is atleast one other picture in the same   access unit with a different valueof nal_unit_type or absentPictureInAuFlag is equal to 1, the value   ofpoc_reset_idc shall be equal to 1 or 2 for all pictures in the accessunit.   The value of poc_reset_idc of a CRA or BLA picture shall be lessthan 3.   When the picture with nuh_layer_id equal to 0 in an accessunit is an IDR picture and there is at least   one non-IDR picture inthe same access unit or absentPictureInAuFlag is equal to 1, the valueof   poc_reset_idc shall be equal to 2 for all pictures in the accessunit.   When the picture with nuh_layer_id equal to 0 in an access unitis not an IDR picture, the value of   poc_reset_idc shall not be equalto 2 for any picture in the access unit.   When the first access unitauA in the poc resetting period has no picture in a particular layerlayerA   or has picture that has discardable_flag equal to 1 in aparticular layer layerA, the value of   poc_reset_idc of pictures in thesubsequent access units following auA, in decoding order, starting  from the first access unit that has picture with nuh_layer_id equal tolayerA until the access unit that   has picture with nuh_layer_id equalto layerA, TemporalId equal to 0, and discardable_flag equal to   0,inclusive, shall be equal to 3. The value of poc_reset_idc of an accessunit is the value of poc_reset_idc of the pictures in the access unit.poc_reset_period_id identifies a POC resetting period. There shall be notwo pictures consecutive in decoding order in the same layer that havethe same value of poc_reset_period_id and poc_reset_idc equal to 1 or 2.When not present, the value of poc_reset_period_id is inferred asfollows:   If the previous picture picA that has poc_reset_period_idpresent in the slice segment header in   present in the same layer ofthe bitstream as the current picture, the value of poc_reset_period_idis   inferred to be equal to the value of the poc_reset_period_id ofpicA.   Otherwise, the value of poc_reset_period_id is inferred to beequal to 0.  NOTE - It is not prohibited for multiple pictures in alayer to have the same value of  poc_reset_period_id and to havepoc_reset_idc equal to 1 or 2 unless such pictures occur in two consecutive access units in decoding order. To minimize the likelihoodof such two pictures appearing  in the bitstream due to picture losses,bitstream extraction, seeking, or splicing operations, encoders  shouldset the value of poc_reset_period_id to be a random value for each POCresetting period  (subject to the constraints specified above). It is arequirement of bitstream conformance that the following constraintsapply:   One POC resetting period shall not include more than one accessunit with poc_reset_idc equal to 1   or 2.   An access unit withpoc_reset_idc equal to 1 or 2 shall be the first access unit in a POCresetting   period.   A picture that follows, in decoding order, thefirst POC resetting picture among all layers of a POC   resetting periodin decoding order shall not precede, in output order, another picture inany layer that   precedes the first POC resetting picture in decodingorder. full_poc_reset_flag equal to 1 specifies that both the mostsignificant bits and the least significant bits of the picture ordercount value for the current picture are reset when the previous picturein decoding order in the same layer does not belong to the same POCresetting period. full_poc_reset_flag equal to 0 specifies that only themost significant bits of the picture order count value for the currentpicture are reset when the previous picture in decoding order in thesame layer does not belong to the same POC resetting period. It is arequirement of bitstream conformance that when the value ofpoc_reset_idc of pictures in the first access unit in the same POCresetting period is equal to 1 or 2, the value of full_poc_reset_flag,when present, shall be equal to poc_reset_idc − 1.

Exemplary Embodiment 2

This embodiment is based on Embodiment 1, with the difference being thatthe derivation of the value of the variable absentPictureInAuFlag is asfollows:

TABLE 2 Exemplary Embodiment 2 When an access unit auA has an IRAPpicture with nuh_layer_id equal to 0 or an IDR picture with nuh_layer_idgreater than 0, the variable absentPictureInAuFlag is derived as followsfor the access unit auA:       If any of the following two conditions istrue, the value of absentPictureInAuFlag is set    equal to 1:         There is at least one picture with discardable_flag equal to 1in the access unit       auA.          There is an access unit auB thatfollows the access unit auA in decoding order       and the access unitauB satisfies one or more of the following conditions:          Theaccess unit belongs to a different POC resetting period than the accessunit         auA.          The access unit has an IRAP picture withnuh_layer_id equal to 0 and         NoClrasOutputFlag equal to 1.         The access unit is the last access unit in the bitstream.      and in addition, there is no picture with a particular value ofnuh_layer_id layerIdA in       the access unit auA, and there is apicture with nuh_layer_id equal to layerIdA that       follows theaccess unit auA in decoding order and precedes the access unit auB in      decoding order.       Otherwise, the value ofabsentPictureInAuFlag is set to be 0.

Exemplary Embodiment 3

This embodiment is based on Embodiments 1 and 2, with the differencebeing that the value of discardable_flag is disallowed to be 1 for IRAPpictures, and the derivation of the variable absentPictureInAuFlag doesnot consider the value of discardable_flag of pictures. The changes tothe slice header semantics with respect to Embodiment 1 are shown below:

TABLE 3 Exemplary Embodiment 3 discardable_flag equal to 1 specifiesthat the coded picture is not used as a reference picture for interprediction and is not used as an inter-layer reference picture in thedecoding process of subsequent pictures in decoding order.discardable_flag equal to 0 specifies that the coded picture may be usedas a reference picture for inter prediction and may be used as aninter-layer reference picture in the decoding process of subsequentpictures in decoding order. When not present, the value ofdiscardable_flag is inferred to be equal to 0. When nal_unit_type isequal to TRAIL_R, TSA_R, STSA_R, RASL_R, 

 RADL_R, BLA_W_LP, BLA_W_RADL, BLA_N_LP, IDR_W_LP, IDR_N_LP and CRA_NUT,the value of discardable_flag shall be equal to 0. ... The change to thederivation of variable absentPictureInAuFlag may be as follows: Thevariable absentPictureInAuFlag is derived as follows:    If 

      

      

 number of pictures in the access unit is less the number of layers inthe bitstream,    the value of absentPictureInAuFlag is set to be 1.   Otherwise, the value of absentPictureInAuFlag is set to be 0. Or,When an access unit auA has an IRAP picture with nuh_layer_id equal to 0or an IDR picture with nuh_layer_id greater than 0, the variableabsentPictureInAuFlag is derived as follows for the access unit auA:   If 

  

     

     

 is an access unit auB that follows the access unit auA in decodingorder and the      access unit auB satisfies one or more of thefollowing conditions:       The access unit belongs to a different POCresetting period than the access unit auA.       The access unit has anIRAP picture with nuh_layer_id equal to 0 and       NoClrasOutputFlagequal to 1.       The access unit is the last access unit in thebitstream.      and in addition, there is no picture with a particularvalue of nuh_layer_id layerIdA in the      access unit auA, and there isa picture with nuh_layer_id equal to layerIdA that follows the     access unit auA and precedes the access unit auB in decoding order.   Otherwise, the value of absentPictureInAuFlag is set to be 0.

Exemplary Embodiment 4

This embodiment is based on Embodiment 1, with the difference being thatthe derivation of the value of the variable absentPictureInAuFlag is asfollows:

TABLE 4 Exemplary Embodiment 4 When an access unit auA has an IRAPpicture with nuh_layer_id equal to 0 or an IDR picture with nuh_layer_idgreater than 0, the variable absentPictureInAuFlag is derived as followsfor the access unit auA:       If any of the following two conditions istrue, the value of absentPictureInAuFlag is set    equal to 1:      There is at least one picture with discardable_flag equal to 1 inthe access unit auA.       There is at least one missing picture in theaccess unit auA. In other words, the following       condition is true.Let auB be the first access unit that follows auA in decoding order and      belongs to a different POC resetting period than the access unitauA, when present. Let       auC be the first access unit that followsauA in decoding order and has an IRAP picture       with nuh_layer_idequal to 0 and NoClrasOutputFlag equal to 1, when present. Let auD      be the first access unit that follows auA in decoding order andhas an IRAP picture       picture in each of the layers in thebitstream, when present. There is no picture with       nuh_layer equalto any particular value of nuh_layer_id layerIdA in the access unit auA,      there is a picture picA with nuh_layer_id equal to layerIdA thatfollows auA in decoding       order, and either none of auB, auC, andauD exists in the bitstream, or the picture picA       precedes, indecoding order, the first of auB (when present), auC (when present), and      auD (when present) in decoding order.    Otherwise, the value ofabsentPictureInAuFlag is set to be 0.Method of Resetting POC

FIG. 8 is a flowchart illustrating a method of coding video information,according to one or more aspects of the present disclosure. The methodrelates to resetting the POC. The process 800 may be performed by anencoder (e.g., the encoder as shown in FIG. 2A, 2B, etc.), a decoder(e.g., the decoder as shown in FIG. 3A, 3B, etc.), or any othercomponent, depending on the embodiment. The blocks of the process 800are described with respect to the decoder 33 in FIG. 3B, but the process800 may be performed by other components, such as an encoder, asmentioned above. The layer 1 video decoder 30B of the decoder 33 and/orthe layer 0 decoder 30A of the decoder 33 may perform the process 800,depending on the embodiment. All embodiments described with respect toFIG. 8 may be implemented separately, or in combination with oneanother. Certain details relating to the process 800 are explainedabove, e.g., with respect to FIG. 4-7.

The process 800 starts at block 801. The decoder 33 can include a memory(e.g., decoded picture buffer 160) for storing video informationassociated with a plurality of layers. The decoder 33 may obtaininformation associated with a current AU to be coded. The current AU cancontain pictures from one or more layers of the plurality of layers.

At block 802, the decoder 33 determines whether the current AU includesa first layer containing an IRAP picture.

At block 803, the decoder 33 determines whether the current AU includesa second layer containing no picture or containing a discardablepicture.

At block 804, the decoder 33 resets the POC of the second layer at thecurrent AU, in response to determining that the current AU includes (1)a first layer that contains an IRAP picture and (2) a second layercontaining no picture or containing a discardable picture. In someembodiments, the decoder 33 resets the POC of the first layer at thecurrent AU, in response to determining that the current AU includes (1)a first layer that contains an IRAP picture and (2) a second layercontaining no picture or containing a discardable picture. In oneembodiment, the first layer is a base layer. In another embodiment, thefirst layer is an enhancement layer and the IRAP picture is an IDRpicture. The decoder 33 may reset the POC of a layer by setting a valueof a first syntax element indicative of whether to reset the POC. In oneembodiment, the first syntax element is poc_reset_idc.

In certain embodiments, the decoder 33, in response to resetting the POCof the second layer at the current AU, for an AU that is subsequent tothe current AU in decoding order, sets the value of the first syntaxelement to indicate that the POC of the second layer was reset at aprior AU.

In some embodiments, the decoder 33 sets the value of the first syntaxelement to indicate that the POC of the second layer was reset at aprior AU for one or more AUs subsequent to the current AU in decodingorder. The one or more subsequent AUs can start with a first AUcontaining a first picture having the same layer ID as the second layerand end with a second AU subsequent to the first AU in decoding ordercontaining a second picture having the same layer ID as the secondlayer, inclusive. In one embodiment, the second picture has a temporalID equal to 0 and is not a discardable picture. In certain embodiments,additionally, the second picture is not a RASL picture, is not a RADLpicture, or is not a SLNR of the second layer.

In certain embodiments, the decoder 33 is a wireless communicationdevice, further comprising a receiver configured to receive video dataaccording to at least one radio access technology (RAT), the video datacomprising the video information associated with the plurality oflayers; and a transmitter configured to operate in accordance with theat least one RAT. The wireless communication device may be a cellulartelephone, and the received video data may be received by the receiverand may be modulated according to cellular communication standard.

In some embodiments, the process 800 may be executable on a wirelesscommunication device comprising: a receiver configured to receive videodata according to at least one radio access technology (RAT), the videodata comprising the video information associated with the plurality oflayers; a transmitter configured to operate in accordance with the atleast one RAT; a memory configured to store the video data; and aprocessor configured to execute instructions to process the video datastored in the memory. The wireless communication device may be acellular telephone, and the received video data may be received by thereceiver and may be modulated according to cellular communicationstandard.

The process 800 ends at block 805. Blocks may be added and/or omitted inthe process 800, depending on the embodiment, and blocks of the process800 may be performed in different orders, depending on the embodiment.

Any features and/or embodiments described with respect to resetting thePOC in this disclosure may be implemented separately or in anycombination thereof. For example, any features and/or embodimentsdescribed in connection with FIGS. 1-7 and other parts of the disclosuremay be implemented in any combination with any features and/orembodiments described in connection with FIG. 8, and vice versa.

Method of Setting full_poc_reset_flag

FIG. 9 is a flowchart illustrating a method of coding video information,according to one or more aspects of the present disclosure. The methodrelates to setting the value of full_poc_reset_flag. The process 900 maybe performed by an encoder (e.g., the encoder as shown in FIG. 2A, 2B,etc.), a decoder (e.g., the decoder as shown in FIG. 3A, 3B, etc.), orany other component, depending on the embodiment. The blocks of theprocess 900 are described with respect to the decoder 33 in FIG. 3B, butthe process 900 may be performed by other components, such as anencoder, as mentioned above. The layer 1 video decoder 30B of thedecoder 33 and/or the layer 0 decoder 30A of the decoder 33 may performthe process 900, depending on the embodiment. All embodiments describedwith respect to FIG. 9 may be implemented separately, or in combinationwith one another. Certain details relating to the process 900 areexplained above, e.g., with respect to FIG. 4-7.

The process 900 starts at block 901. The decoder 33 can include a memory(e.g., decoded picture buffer 160) for storing video informationassociated with a plurality of layers. The decoder 33 may obtaininformation associated with a current AU to be coded. The current AU cancontain pictures from one or more layers of the plurality of layers.

At block 902, the decoder 33 resets the POC of a layer included in thecurrent AU via (1) resetting only the MSB of the POC or (2) resettingboth the MSB of the POC and the LSB of the POC. For example, the POC ofthe layer is reset at the current AU.

At block 903, for pictures in one or more Ails subsequent to the currentAU in decoding order, the decoder 33 sets the value of a first flagindicative whether a reset of the POC is a full reset. In oneembodiment, the value of the first flag is set equal to 0 when the POCis reset by (1) resetting only the MSB of the POC, and the value of thefirst flag is set equal to 1 when the POC is reset by (2) resetting boththe MSB of the POC and the LSB of the POC. The pictures from the one ormore layers in the current AU may have the same POC resetting period. Inone embodiment, the first flag is full_poc_reset_flag. The value of thefirst flag may correspond to the value of a second flag indicative ofwhether to reset the POC. In one embodiment, the second flag ispoc_reset_idc.

In some embodiments, the value of the first flag is set equal to 0 whenthe second flag indicates that the value of the second flag indicatesthat only the MSB of the POC should be reset, and wherein the value ofthe second flag is set equal to 1 when the second flag indicates thatboth the MSB and the LSB of the POC should be reset.

In certain embodiments, the decoder 33 is a wireless communicationdevice, further comprising a receiver configured to receive video dataaccording to at least one radio access technology (RAT), the video datacomprising the video information associated with the plurality oflayers; and a transmitter configured to operate in accordance with theat least one RAT. The wireless communication device may be a cellulartelephone, and the received video data may be received by the receiverand may be modulated according to cellular communication standard.

In some embodiments, the process 900 may be executable on a wirelesscommunication device comprising: a receiver configured to receive videodata according to at least one radio access technology (RAT), the videodata comprising the video information associated with the plurality oflayers; a transmitter configured to operate in accordance with the atleast one RAT; a memory configured to store the video data; and aprocessor configured to execute instructions to process the video datastored in the memory. The wireless communication device may be acellular telephone, and the received video data may be received by thereceiver and may be modulated according to cellular communicationstandard.

The process 900 ends at block 904. Blocks may be added and/or omitted inthe process 900, depending on the embodiment, and blocks of the process900 may be performed in different orders, depending on the embodiment.

Any features and/or embodiments described with respect to setting thevalue of full_poc_reset_flag in this disclosure may be implementedseparately or in any combination thereof. For example, any featuresand/or embodiments described in connection with FIGS. 1-7 and otherparts of the disclosure may be implemented in any combination with anyfeatures and/or embodiments described in connection with FIG. 9, andvice versa.

Information and signals disclosed herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof.

The various illustrative logical blocks, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The techniques described herein may be implemented in hardware (e.g.,computer hardware), software, firmware, or any combination thereof. Suchtechniques may be implemented in any of a variety of devices such asgeneral purposes computers, wireless communication device handsets, orintegrated circuit devices having multiple uses including application inwireless communication device handsets and other devices. Any featuresdescribed as modules or components may be implemented together in anintegrated logic device or separately as discrete but interoperablelogic devices. If implemented in software, the techniques may berealized at least in part by a computer readable medium (e.g., acomputer-readable data storage medium) comprising program code includinginstructions that, when executed, performs one or more of the methodsdescribed above. The computer readable medium may be a non-transitorycomputer readable medium. The computer-readable medium may form part ofa computer program product, which may include packaging materials. Thecomputer-readable medium may comprise memory or data storage media, suchas random access memory (RAM) such as synchronous dynamic random accessmemory (SDRAM), read-only memory (ROM), non-volatile random accessmemory (NVRAM), electrically erasable programmable read-only memory(EEPROM), FLASH memory, magnetic or optical data storage media, and thelike. The techniques additionally, or alternatively, may be realized atleast in part by a computer-readable communication medium that carriesor communicates program code in the form of instructions or datastructures and that can be accessed, read, and/or executed by acomputer, such as propagated signals or waves.

The program code may be executed by a processor, which may include oneor more processors, such as one or more digital signal processors(DSPs), general purpose microprocessors, an application specificintegrated circuits (ASICs), field programmable logic arrays (FPGAs), orother equivalent integrated or discrete logic circuitry. Such aprocessor may be configured to perform any of the techniques describedin this disclosure. A general purpose processor may be a microprocessor;but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration. Accordingly, the term “processor,” as used herein mayrefer to any of the foregoing structure, any combination of theforegoing structure, or any other structure or apparatus suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated software modules or hardware modules configured for encodingand decoding, or incorporated in a combined video encoder-decoder(CODEC). Also, the techniques could be fully implemented in one or morecircuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinter-operative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various embodiments of the disclosure have been described. These andother embodiments are within the scope of the following claims.

What is claimed is:
 1. An apparatus for coding video information, theapparatus comprising: a memory unit for storing a portion of the videoinformation, the portion being associated with a plurality of layers;and a processor operationally coupled to the memory unit and configuredto: obtain information associated with a current access unit (AU) of theportion of the video information stored to the memory unit, the currentAU containing pictures from the plurality of layers; determine that thecurrent AU includes an intra random access point (IRAP) picture from afirst layer of the plurality of layers; determine that the current AUeither includes a discardable picture from a second layer of theplurality of layers or includes no picture from the second layer of theplurality of layers; and reset both a most significant bit (MSB) and aleast significant bit (LSB) of a picture order count (POC) value of anypictures in the first layer or the second layer at the current AU, inresponse to the determinations that the current AU includes the IRAPpicture from the first layer and either the discardable picture or nopicture from the second layer.
 2. The apparatus of claim 1, wherein toreset the POC value, the processor is configured to set a value of afirst syntax element to indicate that the POC value of the second layeris to be reset.
 3. The apparatus of claim 2, wherein the first syntaxelement comprises a poc_reset_idc syntax element.
 4. The apparatus ofclaim 2, wherein the processor is further configured to set, in responseto resetting the POC value of the second layer at the current AU, for asubsequent AU that is positioned subsequently to the current AU indecoding order, a value of a corresponding syntax element to indicatethat the POC value of the second layer was reset at a prior AU of thesubsequent AU.
 5. The apparatus of claim 4, wherein to set the syntaxelement, the processor is configured to set the value of thecorresponding syntax element to indicate that the POC value of thesecond layer was reset at the prior AU for one or more AUs positionedsubsequently to the current AU in decoding order, the one or moresubsequent AUs starting with a first AU containing a first picturehaving a same layer ID as the second layer and ending with a second AUcontaining a second picture having the same layer ID as the secondlayer, wherein: the second picture has a temporal ID equal to zero (0),the second picture is not a discardable picture, and the second pictureis not any of a random access skipped leading (RASL) picture, a randomaccess decodable leading (RADL) picture, or a sub-layer non-referencepicture (SLNR) of the second layer.
 6. The apparatus of claim 1, whereinthe first layer is a base layer.
 7. The apparatus of claim 1, whereinthe first layer is an enhancement layer and the IRAP picture is aninstantaneous decoding refresh (IDR) picture.
 8. The apparatus of claim1, wherein the apparatus is a wireless communication device, furthercomprising: a receiver configured to receive video data according to atleast one radio access technology (RAT), the video data comprising thevideo information associated with the plurality of layers; and atransmitter configured to operate in accordance with the at least oneRAT.
 9. The apparatus of claim 8, wherein the wireless communicationdevice is a cellular telephone and the received video data is receivedby the receiver and is modulated according to cellular communicationstandard.
 10. A method of coding video information, the methodcomprising: storing a portion of the video information, the portionbeing associated with a plurality of layers; obtaining informationassociated with a current access unit (AU) of the video information tobe coded, the current AU containing pictures from the plurality oflayers; determining that the current AU includes an intra random accesspoint (IRAP) picture from a first layer of the plurality of layers;determining that the current AU either includes a discardable picturefrom a second layer of the plurality of layers or includes no picturefrom the second layer of the plurality of layers; and resetting both amost significant bit (MSB) and a least significant bit (LSB) of apicture order count (POC) value of any pictures in the first layer orthe second layer at the current AU, in response to the determinationsthat the current AU includes the IRAP picture from the first layer andeither the discardable picture or no picture from the second layer. 11.The method of claim 10, wherein resetting the POC value of the secondlayer comprises setting a value of a syntax element to indicate that thePOC value of the second layer is to be reset.
 12. The method of claim11, wherein the syntax element comprises a poc_reset_idc syntax element.13. The method of claim 11, further comprising: in response to resettingthe POC of the second layer at the current AU, setting, for subsequentAU that is positioned subsequently to the current AU in decoding order,a value of a corresponding syntax element to indicate that the POC valueof the second layer was reset at a prior AU of the subsequent AU. 14.The method of claim 13, wherein setting the syntax element comprisessetting the value of the corresponding syntax element to indicate thatthe POC value of the second layer was reset at the prior AU for one ormore AUs positioned subsequently to the current AU in decoding order,the one or more subsequent AUs starting with a first AU containing afirst picture having a same layer ID as the second layer and ending witha second AU containing a second picture having the same layer ID as thesecond layer, wherein: the second picture has a temporal ID equal tozero (0), the second picture is not a discardable picture, and thesecond picture is not any of a random access skipped leading (RASL)picture, a random access decodable leading (RADL) picture, or asub-layer non-reference picture (SLNR) of the second layer.
 15. Themethod of claim 10, wherein the first layer is a base layer.
 16. Themethod of claim 10, wherein the first layer is an enhancement layer andthe IRAP picture is an instantaneous decoding refresh (IDR) picture. 17.The method of claim 10, the method being executable on a wirelesscommunication device, wherein the device comprises: a receiverconfigured to receive video data according to at least one radio accesstechnology (RAT), the video data comprising the video informationassociated with the plurality of layers; a transmitter configured tooperate in accordance with the at least one RAT; a memory configured tostore the video data; and a processor configured to execute instructionsto process the video data stored in the memory.
 18. The method of claim17, wherein the wireless communication device is a cellular telephoneand the received video data is received by the receiver and is modulatedaccording to a cellular communication standard.
 19. A non-transitorycomputer readable storage medium comprising instructions that whenexecuted on a processor comprising computer hardware cause the processorto: store a portion of the video information to the non-transitorycomputer readable storage medium, the portion being associated with aplurality of layers; obtain information associated with a current accessunit (AU) to be coded of the portion of the video information stored tothe non-transitory computer readable storage medium, the current AUcontaining pictures from the plurality of layers; determine that thecurrent AU includes an intra random access point (IRAP) picture from afirst layer of the plurality of layers; determine that the current AUeither includes a discardable picture from a second layer of theplurality of layers or includes no picture from the second layer of theplurality of layers; and reset both a most significant bit (MSB) and aleast significant bit (LSB) of a picture order count (POC) value of anypictures in the first layer or the second layer at the current AU, inresponse to the determinations that the current AU includes the IRAPpicture from the first layer and either the discardable picture or nopicture from the second layer.
 20. An apparatus for coding videoinformation, comprising: means for storing a portion of the videoinformation, the portion being associated with a plurality of layers;means for obtaining information associated with a current access unit(AU) of the video information to be coded, the current AU containingpictures from the plurality of layers; means for determining that thecurrent AU includes an intra random access point (IRAP) picture from afirst layer of the plurality of layers; means for determining that thecurrent AU either includes a discardable picture from a second layer ofthe plurality of layers or includes no picture from the second layer ofthe plurality of layers; and means for resetting both a most significantbit (MSB) and a least significant bit (LSB) of a picture order count(POC) value of any pictures in the first layer or the second layer atthe current AU, in response to the determinations that the current AUincludes the IRAP picture from the first layer and either thediscardable picture or no picture from the second layer.
 21. Theapparatus of claim 1, wherein the IRAP picture is a clean random access(CRA) picture.
 22. The apparatus of claim 1, wherein the IRAP picture isa broken link access (BLA) picture.
 23. The method of claim 10, whereinthe IRAP picture is a clean random access (CRA) picture.
 24. The methodof claim 10, wherein the IRAP picture is a broken link access (BLA)picture.